In Elasticsearch, fields can be either 'text' or 'keyword' types. Text fields are analyzed and broken into tokens to support full-text search, allowing you to find documents by words inside the text. Keyword fields are stored as exact values without analysis, making them perfect for filtering, sorting, and aggregations. For example, a 'title' field as text lets you search for words like 'quick' or 'fox', while a 'status' field as keyword lets you filter documents exactly matching 'active'. Understanding these types helps you design your index for efficient search and filtering.