A homogeneous mixture (homo = same) has the same composition throughout. It looks like a uniform substance. Solutions (such as Kool-Aid) are homogeneous mixtures. As long as the correct amount of sugar was used (and there is none settled on the bottom of the jug), then each swallow should taste the same.
On the other hand, heterogeneous mixtures (hetero = different) do not have a uniform composition. Each region has a different property. Salads or trail mixes are great examples of heterogeneous mixtures. Each bite or handful that you take is going to be slightly different.
Because lemonade without pulp is a solution, it is, by definition, a homogeneous mixture. Just like the Kool-Aid, as long as the pulpless lemonade is stirred and made correctly, every swallow should taste the same.
Should the lemonade contain pulp, then the mixture would not be uniform. You may get more pulp in one swallow than you would in another. In this case, the mixture would be considered heterogeneous.