Cirq is a Python library for writing, manipulating, and optimizing quantum circuits and running them against quantum computers and simulators.
This module is cirq-core, which contains everything you'd need to write quantum algorithms for NISQ devices and run them on the built-in Cirq simulators. In order to run algorithms on a given quantum hardware platform, you'll have to install the right cirq module as well.
To install the stable version of only cirq-core, use pip install cirq-core. To install the pre-release version of only cirq-core, use pip install cirq-core --pre.
To get all the optional modules installed as well, you'll have to use pip install cirq or pip install cirq --pre for the pre-release version.