Affricate is a phoneme produced like a stop, but with slow release of the closure, resulting in a fricative ending. The stop part and the fricative part have the same place of articulation (i.e. they are homorganic segments).
In German the combination [ts] is a fricative sound in Ziel 'goal' and Satz 'sentence'. The combination behaves phonologically as a unit in German, in contrast with English where [ts] are two phonemes, cf. hats.