Elasticsearch is an open source, distributed engine for full-text search and analytics. When we need to save data into elasticsearch for searching purposes, we need to understand how the Elasticseach understands our data. If we do not provide guidelines in terms of Elastic Mapping, the Elasticsearch figures it out by itself to the best of its understanding. This means, the Elasticsearch creates default mapping for our data when we save it plus analyzes and indexes the data for searching. It is called default mapping

If the default mapping doesn't serve our purpose of searches i.e., if searches from our data is not as effective as we want then we need to provide mapping while creating index. Mapping is nothing but defining how our document, and its fields, are analyzed, stored and indexed. For example, use mappings to define: which of our document's string fields are to be considered as full text fields. which fields are of type numbers, dates, or geolocations. the format of date values. Also, we need to define rules how the new fields, which are not specified in the original mapping, should be treated if ingested after proving mapping.