A collision domain is a network segment connected by a shared medium or through repeaters/switches where data packets may collide with one another while being sent. The collision domain applies particularly in wireless networks, but also affected early versions of Ethernet. A network collision occurs when more than one device attempts to send a packet on a network segment at the same time. Members of a collision domain may be involved in collisions with one another. Devices outside the collision domain do not have collisions with those inside.
Since every port in a switch is its own collision domain, a host will never collide unless it's medium is running half duplex.
That is why a switch segregates collision domains, because every port is an individual collision domain.