From Halopedia, the Halo wiki
An audio log is a collectible recording that sheds light on lore, the plot, or individual characters. Audio logs have been featured in several titles, starting with Halo 3: ODST.
Audio logs can be found in several forms within the games, most notably:
This is a disambiguation page — a navigational aid which lists other pages that might otherwise share the same or a similar title. If an article link referred you here, you might want to go back and fix it to point directly to the intended page.