equally likely means as likely as the other side ex: 1 piece of candy on this side,1 piece of candy on that side
The two events have the same probability of happening.
1/4
If you are using it in terms of an event (aka rolling a dice, flipping a coin, etc.) it means there is a 50% chance of it happening and not happening. It can be equal to 50% or 1/2 or anything equal...
http://www.emathzone.com/tutorials/basic-statistics/definition-of-probability.html