The term "gat line" can refer to a number of things, such as a railroad track, a military fortification, or a line of fencing. Synonyms for this phrase include "track line", "defense line", or "fence line". In the context of a railway, it can also be referred to as a "trackway", "railroad line" or "train line". For a military fortification, it can be known as a "fortification line" or "defensive line". Similarly, a line of fencing can be identified as a "boundary line" or "property line". Regardless of the specific usage, there are always alternative phrasing options available to suit the situation.