The Quick Electronic Component Guide
If you've ever had to buy a resistor, a transistor, a capacitor, or any such part, you've seen how many choices there are. This page is not a complete guide to every one of those details, but it is a primer on some of the more important ones.
What good is a part if you can't connect anything to it? Components have connection points (pins or more generically terminals) that are used to tie them to other circuit elements. These may take a number of shapes.
PC mount terminals have small pins intended to go through a printed circuit board (PCB). Holes are made in the board through which the pins are inserted, and then they are soldered into place. These switches also often have posts or some other mechanisms to help firmly mount them to that board.
Through-hole terminals have larger, thicker, terminals than PC mount. Generally the terminals are rectangular in shape, with rounded ends. Their terminals are much sturdier and can easily hold the switch in place with no additional support.
Surface mount terminals have small tabs that jut out to the sides, or small pins that wrap around the sides to provide a surface to solder to, or just flat metallic areas on the sides. They are meant to be placed next to a solder pad on a PCB and then soldered to it. This configuration is very small, and doesn't require going through all the PCB layers the way regular PCB mount terminals do. However, it is not very strong.
Solder lug terminals are not intended for PCB mounting. They generally are mounted to the case. Their terminals are relatively large and have holes drilled through them; in typical use, a wire is run through this hole once or twice (to hold it in place during soldering and in use) and then it is soldered into place. These terminals produce very sturdy connections.
Solder tab terminals have thin, often flexible metal tabs with no holes through them. Wires can be soldered to their surface. It is very easy to desolder this connection and resolder a new part in, which is why batteries sometimes have solder tabs.
Solder well terminals have shallow indentations called "wells" that provide a concave metal surface. A wire is placed in the well and then soldered into place. This can allow a very dense packing of terminals and is sometimes used in complex switches.
Screw terminals have relatively large screws, which you are meant to wrap a wire around before tightening. This is a very strong hold, and yet is relatively easy to detach if needed. It also provides a lot of surface area between the wire and the terminal, which makes it well-suited to higher voltage applications. Devices that connect to mains power (light switches, wall outlets) often use screw terminals.
It's all well and good to get your device wired up, but you don't want it flopping around, do you? So you need to secure it to something. That is, mount it.
Surface mount components are the smallest. As described above, they usually are just held in place by solder attaching them to the PCB. This is a very easy mounting method (all you have to do is solder the component down, which you needed to do anyway), but cannot support a great deal of weight. Surface mounts come in a variety of sizes, ranging from small to wow-that's-really-small.
PCB mount (or board mount) components, also as described above, are meant to mount to a circuit board. This may just mean they have pins that go through the board and are soldered in place, or they might have additional supports. Those supports are sometimes larger metal posts that also go through the board and are soldered into place, and sometimes are plastic clips that go through the board and then lock into place. The plastic clips are notoriously irritating to remove.
Case mount or panel mount components are intended to attach to the case of the device they are in (or its front panel). They usually snap or screw into place. This mounting method is generally bulkier, but can be made very sturdy.