I mean what the basic term entails: defense of a position with information. There's an apologetics forum here, specifically Xian in nature. I suppose you could mean apologetics for other faiths, but that's not what's at issue here.
Here's a quick summation of presuppositional apologetics, though it has a more detailed Wikipedia article
Presuppositional apologetics claims that presuppositions are essential to any philosophical position, and that there are no "neutral" assumptions from which a Christian can reason with a non-Christian.[38] There are two main schools of presuppositional apologetics, that of Cornelius Van Til (and his students Greg Bahnsen and John Frame) and that of Gordon Haddon Clark.
Van Til drew upon, but did not always agree with, the work of Dutch Calvinist philosophers and theologians such as D. H. Th. Vollenhoven, Herman Dooyeweerd, Hendrik G. Stoker, Herman Bavinck, and Abraham Kuyper. Bahnsen describes Van Til's approach to Christian apologetics as pointing out the difference in ultimate principles between Christians and non-Christians, and then showing that the non-Christian principles reduce to absurdity.[39] In practice this school utilizes what has come to be known as the transcendental argument for the existence of God.
Clark held that the Scriptures constituted the axioms of Christian thought, which could not be questioned, though their consistency could be discussed.[38] A consequence of this position is that God's existence can never be demonstrated, either by empirical means or by philosophical argument. In The Justification of Knowledge, the Calvinist theologian Robert L. Reymond argues that believers should not even attempt such proofs.