CMIS stands for
Content Management Interoperability Services. Using CMIS within Python scripts is a handy way to export/import data from/to Alfresco (or any other CMIS-compliant document management system) or do mass updates of data within Alfresco. This can be changes to document attributes or even changes to the documents themselves. If you come from a relational database background, think of CMIS scripts fulfilling a similar role with Alfresco as SQL scripts do with relational databases.
cmislib from Apache Chemistry is a CMIS client library for Python. This tutorial shows you how to install Python and CMIS on a Ubuntu computer.