What does 'exploratory committee' mean?

Former Gov. Tim Pawlenty's creation of an exploratory committee Monday does not mean he is a presidential candidate, but he does have to start playing by most rules governing them. In this phase, Pawlenty:

• Can start raising money for a presidential bid, subject to federal contribution limits.

• Will have to reveal his fundraising numbers if he declares his candidacy.

• Cannot call himself a candidate or advertise his intention to campaign.