SerDe is a short name for Serializer/Deserializer. In Hive, SerDe is used for input/output interface. For any communication we have to Serialize and Deserialize the data.
With SerDe, Hive can read data from a table and write it to HDFS in a custom format. We can also implement custom SerDe to handle our own data formats.
During map and reduce, Hive can use serialize methods of LazyBinarySerDe and BinarySortableSerDe.
We can also use ObjectInspector, for a SerDe to serialize an object created by another SerDe.