Side Bets - what are they

Sometimes the pot gets segmented into (up to 3??) separate amounts.
I have had a search on here & cannot figure out why this happens.

When the betting exceeds one of the playes total chip stack a side pot is developed between the 2 players that still have chips to play with. The player with the smaller amount is only playing for the main pot while the other players are playing for both . There can be more than one side pot if it enough players are in the hand.

lets say
player A is all in and has $4.00
player B raises all in but has $7.00
Player C call both

So Pot #1 has 3x $4.00 bets = $12.00 includes all 3 players who play for pot
Side pot #2 has 2x $3.00 bets = $6.00 includes player B and C only
hope this helps

So basically, we have a main pot and side pot/side pots.
Side bets therefore are bets occur only on side pot/side pots.

Thanks very much, this explains it.