Migratory describes living things that move from one place to another, often with the seasons, and often come back later. The collocation you will meet first is migratory birds: birds that spend the cold months in a warm country and fly home in spring. Scientists also talk about migratory fish, such as salmon, that swim a very long way to lay eggs. People can be migratory too — migratory workers go where the jobs are — but that use is more formal; in everyday talk we usually say migrant. Though actually, migratory is about the moving itself, again and again, not about settling. An immigrant has come to live in a new country; a migratory animal is still on that regular journey. It is an adjective: a migratory bird, migratory patterns. You will hear it in nature programmes and in geography class more than in casual chat.