It gets stale.
If you are using an already prepared masa mix (masa preparada) then there should already be a sufficient amount of fat (either vegetable shortening or lard (manteca)) in the mix. However, if you're preparing your masa from a dry meal then you will need to mix it with one of the previous ingredients to get the corn meal to hold together during the preparation and cooking process. Many say that lard adds a flavor that can't be replicated with shortening. However, because of concerns with the amount of saturated fats in lard, using shortening can be beneficial and make the density of the masa easier to work with. If using shortening it's probably best to "season" your masa by adding roasted chiles (poblano for flavor and chipotle for heat) or other seasonings (like cumin, garlic, lime juice and salt, for example).
Most likely
Masa Perttilä was born in 1896.
Masa Perttilä died in 1968.
Masa Yamaguchi was born in 1974.
Masa Nakayama was born in 1891.
George Masa died in 1933.
George Masa was born in 1881.
Masa - restaurant - was created in 2004.
Masa Niemi is 152 cm.
Lance Masa is 5' 7".