Feel free to mock or make fun of me in all the ways you prefer, I perfectly know that I deserve it.
What is a Buffer?
Since I started this whole thing...
In the simplest (not-quite-100%-complete-and-accurate) terms, a buffer is a small amplifier that's used to boost the signal from your bass as it travels through all the cables, pedals, and wiring that are between your bass and your amp.
Many older pedals (and we're talking '60s-'70s: mostly classic wahs and fuzzes) were known for "tone-sucking" (or stealing a lot of the high-end from your signal), when they weren't switched on. Newer conventional (i.e.
not true-bypass) pedals (Boss, Ibanez, etc.) generally include a buffer (small amp) that sends your signal through the pedal when the effect is not in use. Some of these buffers sound great, some...not so much.
If you use a lot of vintage or conventional pedals in your setup, the signal can be degraded before it reaches your amp. A string of conventional pedals with crappy buffers can also amplify each other's noise, further hurting your tone.
Enter true-bypass, where the signal is hardwired straight through the pedal when not in use. Theoretically, this eliminates most of the effects (hah!) that an inactive pedal would have on your tone. Unfortunately, putting a dozen true-bypass pedals (and patch cables) between your bass and amp is essentially the same thing as using a super-long cable, which can also rob some of your signal. So, all a buffer does is boost your signal so it can survive the long trip without losing its zing.
There's more to it (impedance, capacitance, etc.), but that's the gist. Here's
a great article (on a fantastic site) that gives a little more in-depth explanation.
You can also search here on TB, especially in the Effects forum. Lots of good info.