In the realm of solid axle suspension, the job of your links or control arms is to hold your axle in place throughout suspension travel. There are many ways to accomplish this all with their inherent flaws and strong points which i will briefly cover. This is a 1% depth overview of all points.

Links/Control Arms: A bar of a set length with movable joints at either end

Lower Links: These connect your axle to your frame and go front to back when viewed from the side, they are below your upper links

Upper Link(s): Yup exactly, but above the lowers

Panhard/track Bar: A link that connects the axle to the frame laterally, if looking at a vehicle from the front this link will go side to side

Heim Joint/Uniball: This is a joint design with a circular "race" or cage that holds a steel ball. The race can be made of steel, bronze, or even poly-urethane (like Johnny Joints). There are many different types but their design is to allow angle changes in a bolted linkage.

Drag Link: This is a steering component, it's a link that connects the pitman arm (the arm attached to the steering box) to the steering knucle of the axle.

Tie Rod: This is also a steering component, it connects 1 knucle to another.

Caster Angle: Think of the front wheels of a shopping cart, as you push the cart the wheels can turn but want to say behind the axis they are turning on. This effects return to center and steering feel, especially on the road. More caster will generally create stronger return to center and has a heavier steering feel, it will also track straighter. There is also Toe, Ackerman Angle, and KPI that all relate to steering feel, traction in a corner, and steering quickness, which may be covered in another article.

Instant Center:The point at which your suspension moves about. Looking at the vehicle from the side, it's an imaginary point in space where the upper and lower links converge.

Anti Squat: The suspension resistance to squatting under acceleration. It's expressed as a percentage such that 100% anti squat means the suspension will not squat under acceleration. 0% means it has no resistance to squatting under acceleration and all the force is transfered into the springs/shocks. Below 0% (often call pro-squat) means it will squat even more than the normal amount of force created. A good way to think about this is as weight transfer, how much of the weight transfer is absorbed by the link geometry versus how much goes into the springs/shocks.

Anti Dive: Same as anti squat but think of it as weight transfer from braking which occurs on the front end.

Anti-lift: The opposite of squat or dive, the suspension resistance to lifting under acceleration or braking. Useful to think about as the resistance to the opposite forms of weight transfer.

Pinion angle: The angle of your axles pinion flange. In the front this is tied to your caster angle as the 2 are fixed. I find it's much easier to think about caster angle changes throughout travel than pinion, provided the pinion angle does not get wild due to a short front driveshaft or excessive angle to start with.

Driveshaft Plunge: Though not as much of a concern in rock crawlers or lower horsepower rigs, this is how much your driveshaft slip joint has to move in and out throughout travel. In high horsepower applications when hitting whoops at speed the shock loading with lots of plunge will shred your splines or destroy your output shaft bearings on the transmission. This is also less of an issue with automatic transmissions as the torque converter acts a a bushing with the viscous coupling to reduce the agressiveness of the shock load.

Radius Arms are stock on modern day 1 ton trucks with live front axles. 05+ super duty axles will have radius arm mounts built into the front Dana 60 axle itself. Both the upper and lower link mounts at the axle side are part of the same link. Some aftermarket designs will incorporate a joint of some kind which in essence attaches the "upper link" to the lower link. There are also some goofy variants that let you unlock one sides upper link to allow it to articulate freely, and there have even been designs that use a firmly valved shock as the upper link on one side.

Pros:

Easy to install, super duty axles already have the mounts on them.

You don't have to worry about suspension geometry.

Binding can increase on road driveability, they can act like a sway bar and typically have benign handling characteristics.

Cons:

Binding limits articulation as seen in the video below:

You cannot design a caster curve or any meaningful geometry into the system like other link setups.

Has a propensity to wheel hop

The most popular solid axle swap front suspension link orientation. 1 upper link can be easier to package however having only one upper link and additionally putting it on the drivers side can induce more "torque lean". This is especially frustrating with driver drop differentials as keeping the driveshaft and upper link on the same side makes it really easy to land a 3rd leg for your skid plate on the passenger side.

3 points of attachment are always perfectly planar, imagine a table with 3 legs or a tripod... all 3 legs will always be touching the ground. If a table has 4 legs it can teeter toter. Points always go down a dimension so 3 points are always 2 dimensional, 4 points are 3 dimensional etc. Because of this 3 links cannot bind, even with a panhard pulling them side to side, outside of poor link bracket orientation that makes physical contact with something.

Pros:

Cannot Bind

When the panhard is aligned with the drag link this suepsnion design eliminates or reduces bump steer with a manual steering linkage

Easy to package

Suspension geometry can be set throughout travel based on the vehicles usage and desired shock tuning

Cons:

Torque lean from having 1 upper link

Side to side sway from panhard bar locating axle

Can drive poorly on road unless well designed

This is probably the most common rear suspension on modern SUV/Pickups. It uses 2 upper links, 2 lower links, and a panhard bar that locates the axle side to side. As mentioned before, a 4 link with panhard exists in a state of bind. The more the links are triangulated and the shorter they are the more this bind occurs. For suspension design purposes, every suspension is binding at all times... If a joint has any resistance to movement that is bind. A more useful way to think about binding is as if it is spring rate. OEM engineers will actually design this binding/spring rate in to suspensions to increase handling.

Pros:

Though not something you can see in a link calculator, the addition of the second upper link does make all driving characteristics generally more benign.

I often hear the benefit is that if one of your upper link breaks, the suspension still works. For how often i hear it, It just makes no sense to me... you can literally calculate the loads on the upper link and just build it with enough safety factor that It's not an issue. Also, why not run 2 panhards then?

Cons:

Torque lean from having 1 upper link

Side to side sway from panhard bar locating axle

Can drive poorly on road unless well designed