When we observe two or more terrestrial prominent objects in a line it is called a transit bearing.
The transit bearing of these prominent objects are sometime joined by a line and true bearing is mentioned on chart otherwise we can use the parallel ruler to see their transit bearing value and compare with compass bearing taken from vessel to obtain compass error
In other words transit bearing can also explained as:
When two charted objects come into line they are said to be in transit. It has already been shown how a transit can be used to check the compass error. A transit can also be used to obtain a fix in conjunction with another position line such as a range (or be used to obtain a fix in conjunction with another position line such as a range (or even a sounding) without use of the compass.