Every meridian of longitude begins and ends at the earth's poles.
You can consider whichever one you prefer to be the beginning.
By international agreement about 200 years ago, the zero-reference line of longitude is the Prime Meridian.
All lines of longitude are equally long, beginning and ending at the poles.
A line of constant longitude is often referred to as a 'meridian'.
another name for a line of longitude is meridian.
A Line of longitude is an invisible line going north to south on the earth. The main one is called the prime meridian.
meridian
You're thinking of the International Date Line -- ~180 degrees of longitude -- which is not a straight line, because of politics.
The 0' line of longitude is called the Greenwich Meridian because it passes through Greenwich, Lonon
International Date Line
The so-called 'lines' of longitude are also called 'meridians'. The Prime Meridian is a line of longitude. It's the line made out of all the points on Earth whose longitude is zero.
Any line that joins the north and south poles has the same longitude at every point on it. It's called the 'meridian' of that longitude.
The Prime Meridian