Islamophobia is more or less bigotry towards Islam or Muslims. Of course that probably depends on what is defined as "bigotry"...
But the main point about Islamophobia can be summarized as follows:
1) An Islamophobe will insult Muslims or Islamic beliefs just to offend. An example might be a novel being written in which the Prophet's wife is portrayed in less than savory manner. Such a book serves little to no benefit to humanity asides from maybe entertainment, and even that is subjective.
2) An Islamophobe will apply standards to Islam or Muslims that they do not hold for themselves (or others).
3) An Islamophobe will actually invent false statements or attribute falsities against Islam or Muslims.
In my personal opinion, that pretty much covers what Islamophobia is. Its common sense for themost part. It should bear noting that one only needs to fulfill any single one of those 3 things in order to be reasonably considered an Islamophobe.
Simply disagreeing with Islam or Muslims is NOT islamophobia. For example the statement "there is nothing wrong with drinking alcohol" is NOT islamophobic, but "muslims are idiots for not drinking alcohol" is an islamophobic statement.