Like Terms.

Like terms are numbers that can be combined.
For example 1w + 2w are considered like terms because they have the same variables. (w)
Another example is 1p + 2w are not Like terms. P and W are not the same thing.
So in that case we can't combine them. If we was to do that problem the answer will be the same thing. The reason it will be the same thing is because we can't combine them so therefore we leave it the same way it came.