Im going to be banded on 7/29, and while reading the site i keep hearing about PBing. what is it and why does it happen and when does it usually happen?

It's when the food comes back up right after you eat it and you almost throw up.

A PB is a bandster term for "productive burp" which happens thusly:

Usually once you have good restriction, but possible any time, if you eat too large a bite, don't chew well enough, or are overfull, the bite of food can't fit through your stoma (hole formed by the band between your "pouch" or upper stomach and your lower stomach) and it has to go somewhere, so it comes back up. The esophagus isn't built to have things just sit there, it's a conveyor belt that likes to move things along. So it will spasm...and if the food doesn't go on through, the body produces a lot of mucous (called slime here) which lubricates the esophagus and offending bolus of food and helps move it up and out.

it is different from vomiting in that there are usually no stomach spasms involved, and there is no stomach bile/acid expelled.

It can be dangerous if you PB too strongly or too much at first, before your band is healed, and later on even if healed, if you PB a lot (some do it daily as a way of life) it is very hard on your innards and can cause the band to slip. An occasional misstep/PB, however, especially if it happens after you've healed from surgery, isn't really a cause for concern but it should be a lesson to be learned.

They are almost always caused by "operator error"...not chewing well, bite too big, or overeating. Occasionally, though, a PB is caused by being too tight (too much fill) and if that's the case, you need to get a little saline removed quickly or risk poor weight loss/weight gain, problems with your band, etc.