When indexing data in Elasticsearch, the Analyzer assigned to the index internally transforms the data. An analyzer, in essence, specifies how text should be indexed and searched in Elasticsearch. Elasticsearch includes a number of ready-to-use analyzers. Custom analyzers can also be created by combining the built-in character filters, tokenizers, and token filters.  Character Filter: A tool for removing or changing unused characters.  Tokenizer: A programmed that divides or breaks text into tokens (or words) based on certain criteria (e.g. whitespace).  The token filter receives tokens and applies filters to them (such as changing uppercase terms into lowercase).