Tetrad: A tetrad is a four-part structure that forms during the prophase of meiosis and consists of two homologous chromosomes, each composed of two sister chromatids.
Synapsis: Synapsis is the pairing of two homologous chromosomes that occurs during meiosis. It allows matching-up of homologous pairs prior to their segregation.
Chiasmata: Chiasmata are the points where crossing over occurs between two nonsister chromatids in a tetrad during meiosis.