Apache Solr is an open-source search platform that is used to index and search large volumes of text-based data, such as web pages, documents, and databases. It is based on the Apache Lucene search library and provides a REST-like API for indexing and querying data.
Solr provides a number of features that make it a popular choice for search applications, including support for faceted search, full-text search, hit highlighting, spell checking, and geospatial search. It also includes a powerful query language that allows users to construct complex queries to find the information they need.
Solr can be used as a standalone server or embedded within a Java application. It is widely used in a variety of industries, including e-commerce, media, healthcare, and government.