2500 calories is a meal, not a day.
well said hoose.
To answer your other question about "what is bulking and cutting", it basically refers to bodybuilders eating a ton during the offseason to really put on as much mass as possible. During this time they don't worry too much about fat gain, as it's an inevitable consequence of eating so much.
Cutting is when (usually pre-contest but really just anytime they want) they decide to burn off the fat they've gained in order to show off the muscle they've built, by drastically reducing calories and carbs, and increasing cardio.
It's a pretty old school approach, and it certainly works, but there's a downside too. For one thing, people usually way overestimate how much muscle they've built and underestimate how fat they've gotten. Leads to disappointment once they cut down. Also, a lot of people can't handle the idea of deliberately letting themselves gain bodyfat. They want to rock those hot abs year round. Also, it's not really very good for you to carry round loads of fat, regardless of how much muscle you have. Lots of people use the "I'm bulking" excuse to eat fast food five times a week and ruin their health.
If you are looking to get huge, an all out bulking assault where you don't care about fat gain is definitely the way to do it. For average joes like us though, you're as well just increasing your calories a bit and staying lean. There's always going to be a bit of fat gain when you're trying to get bigger, but if you're smart you can keep it to a minimum.