The term "gauge" has several meanings, depending on its context.
1) In general usage, a gauge is an instrument or device used for measuring or checking something, such as a carpenter's level which helps to ensure that a surface is flat and level.
2) In the field of transportation, particularly railways, "gauge" refers to the distance between the rails on a track. This measurement determines whether a train can run on a particular railway line or not. For example, if a railway has an "standard gauge," it means that its tracks are spaced 4 feet and 8.5 inches (147 cm) apart.
3) In medicine, a "gauge" refers to the size of a wound or incision, usually measured in fractions of an inch or centimeters. For example, if a doctor makes a gauge of 2 inches with a scalpel, it means that they have cut into the skin to a depth of two inches.
4) In the field of meteorology, "gauge" refers to an instrument used for measuring precipitation, such as rain or snowfall. These instruments are usually placed outside and collect data over time which can be used to calculate how much water has fallen from the sky.