It is said that scientists use only uniformitarian explanations for the world's rocks. That is, all their explanations invoke slow, gradual geological processes. For example,
"...polystrate trees (trees extending through two or more strata, each of which, according to evolutionary interpretations, was deposited slowly over a long period of time)."
--Duane Gish, Creation Research Society Quarterly 12(1):34-46 June, 1975
Young-Earth Creationists are catastrophists. Their explanations involve a small number of rapid, global events, such as the Flood.
Uniformitarianism was started in 1795 by James Hutton's Theory of the Earth. The idea was championed by later authors, such as Charles Lyell, and basically what they meant was that the past should be explained by processes which can be seen in the present day.
Some geologists of Lyell's school did indeed carry things too far, and insist on only slow, gradual processes. The residue of that, in the 1900's, was mostly the attitude that catastrophe explanations should not be used until other explanations were ruled out. But it's not worth arguing about the views of long-dead scientists. The important point is what living ones say.
They know from recent history that volcanoes can make abrupt changes to landscapes, and that a river flood can dump yards of mud in the space of days. So, it is obvious that some rocks formed more quickly than others. Lyell himself said so in 1830 in his Principles of Geology.
In the last few decades, there has been much more appreciation of this variability of rate. We now explain the scablands of Washington by the sudden bursting of a huge glacial dam. It is now a common idea that a meteorite killed off the dinosaurs. We also appreciate that conditions were once different. For instance, the atmosphere of the early earth had no free oxygen.
So, modern geology is not just about slow, gradual processes. That said, it is clear that slow processes exist. For instance, the Santa Barbara basin is today acquiring sediment at one foot per century.
Physicists sometimes use the same word. When they use it, they mean that reality is lawful - that there is some set of laws which uniformly apply everywhere, and which have always applied.