Tom Leoni describes a partisan as:
The origins of this weapons are unknown, although it is undoubtedly a variant of the traditional spear. It was in vogue between the 16th and 17th Centuries, used alone or in conjunction with the large round shield, or rotella. In this last guise, it was a Renaissance reincarnation of the classical hoplite weapon-combination. The partisan could be either wielded firmly in the hands or cast from a single-handed grip. Typically, it features a rather long triangular thrusting blade with a more or less pronounced center-ridge. At the base of the blade, there are usually two small projections or lugs. The partisan should be mounted on an octagonal-section shaft.
This description can be found in his article titled The Magic of Polearms.