beginning of a line
Refers to the start of a line of text, code, or writing. Common in computing and document editing contexts.
Please move the cursor to the beginning of the line.
In this editor, you can insert an indent at the beginning of the line.
先頭 is a more general term for 'head' or 'front' of something, while 行の先頭 specifically refers to the start of a line.
Compound of 行 (line) + の (possessive particle) + 先頭 (head, beginning). The exact historical derivation is straightforward; the phrase is a transparent combination of its parts.