What is the name of the beginning of longitude lines?

Answer 1

All of the longitude "lines" merge at the north and south poles, so you might say that they 'start' at one of these points and end at the other one.

If the question means to ask: "Where is the line of zero longitude ?", then the answer is:

The origin of longitude is defined as the Prime Meridian, an imaginary line between the north and south poles that passes through the Royal Observatory in Greenwich, England.

Answer 2

The lines begin and end at the Poles. Longitude begins at the Prime Meridian.

Answer 3

The prime meridian is the name of the beginning of longitude lines. This imaginary line runs from the North Pole to the South Pole and is designated as 0 degrees longitude.