terrain-n; 3 Senses

Sense Number 1: tract of land, geological expanse of land

Commentary: TERRAIN[+expanse][+geographical][+land]

John's so-called all-terrain vehicle got stuck in the mud.
We hiked through some tough desert terrain.
The edge of town had become so developed that it was now unfamiliar terrain to Bob. (refers to physical area, layout)

WordNet 3.0 Sense Numbers: 1

Sense Number 2: knowledge domain

Commentary: TERRAIN[+expanse][+symbolic][+domain][+knowledge]

Quantum gravity is unknown terrain to most of the members of this audience.
Mary felt on familiar terrain when the conversation turned to music.
His paper covers some new terrain in the field of automated drug discovery.

WordNet 0.0 Sense Numbers: 3

Sense Number 3: a uniform geological formation bounded by a fault

Commentary: TERRAIN[+entity][+structure][+geological][+bounded][+fault][+stratigraphy]
NOTE: a narrow, specialized sense of Sense 1
NOTE: variant spelling of this sense is: 'terrane'

The geologist noted where the limestone terrain ended and the igneous rock began.
Figure 2 shows a large terrane of granite, flanked by a block of shale.

WordNet 0.0 Sense Numbers: 2