Intel are information you can buy to help in your missions, this can range from information collecting like dossiers to helping your missions directly. You can buy them in the Clearinghouse from anonymous source or dealers and people you have known.
During his mission, Michael Thorton can come across documentation and records regarding other characters and factions, friend or foe alike. Information regarding people or factions are compiled as dossiers. There is also available intel on his current mission: security details or surveillance and mapping of where he's going. This intelligence can be bought off of The Clearinghouse for various sums of money.
When intel is bought, Mike posts on The Clearinghouse what he's looking for, somebody will email him and send him the details he needs.