A campaign is any series of actions or events that are meant to achieve a particular result, like an advertising campaign of television commercials and Internet ads that tries to convince kids to buy bubble gum-flavored toothpaste.
The noun campaign describes any group of actions that are done with an ultimate purpose in mind. The goal of a political campaign is to put a candidate in office. The goal of a military campaign might be to take over a city, as in General Sherman's Civil War campaign to capture Atlanta. Campaign can also be used as a verb, like when an environmental organization campaigns to prevent a developer from building a shopping mall by asking people to sign petitions and soliciting their members of congress.