Every business in France is classified under an activity code entitled APE - Activite Principale de l’Entreprise - or NAF code. When registering your company, you will need to indicate which is your main activity using an APE code. Here is the APE list in English up-dated by the national Institute of statistics INSEE.
For example, if you sell online your APE code would be 97.91B - vente a distance sur catalogue specialise. Another example, if you plan to become an IT consultant specialised in hardware and software your APE code would be 62.02 - conseils en systemes informatiques.
Here's how to add an APE code to your business in France (podcast).