What is a custom analyzer in Elasticsearch?

A custom analyzer allows you to compose your own analysis pipeline by combining a tokenizer, character filters, and token filters to suit your specific search needs. Define it in the index settings under analysis.analyzer. For example, an autocomplete analyzer might use the edge_ngram tokenizer to generate prefix tokens (e.g., "ela", "elas", "elast") for fast prefix matching. A synonym analyzer might add a synonym token filter to map "laptop" to "notebook". A language-specific analyzer might use a stemmer and stop word filter for that language. Custom analyzers are one of the most powerful tools for improving search relevance and performance.