The International Patent Classification system (IPC), established by the Strasbourg Agreement 1971, is a hierarchical system which uses language-independent symbols to classify patents and utility models according to the area of technology to which they relate.
The technical content of almost all the patent documents published worldwide is classified using this system.
IPC classification symbols are made up of a letter denoting the IPC section (e.g. A), followed by a number (two digits) denoting the IPC class (e.g. A63), then a letter denoting the IPC subclass (e.g. A63B). A number (variable, 1-4 digits) denotes the IPC main group (e.g. A63B49). This is followed by a forward slash "/" and a number (variable, 2-6 digits) denoting the IPC subgroup (e.g. A63B49/02).
Please see espacenet for more details.