The title comes from the word "Ilion," which is an alternate name for Troy and not an alternate name for a lion. (Technically, "Troy" is the surrounding state; Ilion is more like the state capital.) So the Iliad means "the thing about Ilion."
If that sounds pretty lame, just remember that this title, like the poem's division into 24 Books, probably comes from a later tradition than the original epic. For a better idea of what the poem's about, in its own words, look at its opening line: "Sing, goddess, the anger of Peleus' son Achilleus."
The goddess here is the poet's muse. Homer is asking her for insight into his subject matter: the hero Achilleus, his anger, and its terrible fallout.