While some plants are capable of self pollenization, the term is more often used in pollination management as a plant that provides abundant, compatible, and viable pollen at the same time of bloom as the pollenized plant. For example most crabapple varieties are good pollenizers for any apple variety that blooms at the same time, and are often used in apple orchards for the purpose. Some apple varieties produce very little pollen; some produce pollen that is sterile, or incompatible with other apple varieties. These are poor pollenizers.
A pollenizer can also be the male plant in the case where entire plants have gender, such as with kiwifruit or holly.
Plants are sometimes mistakenly called pollinators. A plant can only be a pollinator when it is self fertile and it physically pollinates itself without the aid of an external pollinator. For example some nursery catalogs may say x variety should be planted as a pollinator for y variety, when they actually are referring to it as a pollenizer.
Note: pollenizer is the most common spelling; occasionally one sees the alternative pollinizer.
See also: Pollination