A defined group of contacts, chosen by attributes or tags, that a campaign is sent to instead of the whole contact list.
A segment is a slice of your contacts that share something: they live in a certain city, bought a certain product, joined in the last month, or carry a particular tag. Campaigns go to a segment rather than to everyone.
Segmenting is the single most effective way to keep broadcasts relevant. A customer who receives an offer for something they actually use is far less likely to block you than one who receives everything you send. Better relevance protects your quality rating, and with it your ability to keep messaging.
Keep the data clean enough to segment on: store useful attributes when contacts are imported or when a chatbot asks a question, and tag contacts consistently. In Marichi Talks, segments are built from your contact book's attributes and tags and used to choose who a campaign goes to.