Unlike English TV shows Anime have set periods of time where all of the new releases start and end around the same time (usually within a week or so) and are seasonal coming out four times a year.
Winter (January - March)
Spring (April - June)
Summer (July - September)
Autumn/Fall (October - December)
There are some exceptions to this as different Anime's have different amounts of episodes but are usually in sets of 12 or 24 so they may overlap slightly.
