It's not as popular as Protocol Buffers, Thrift, MessagePack etc., probably because it started out in Java land (I believe it came from Doug Nutch of Lucene fame).

I've never used it, but one benefit of Avro is that it can embed the schema in the serialized output, which allows clients to consume data even though they don't have the IDL, which isn't possible with Protobuf and Thrift. MessagePack does include types and map keys, but doesn't have a schema.

Looks like a data serialization format: https://avro.apache.org/

(Never heard of it either)

It allows you to define a schema, and then compile it to various languages and have multiple applications in multiple languages "speak" the same class, down to the binary level (for RPC, blob storage etc).