What does a sister line mean in palmistry?

What this means

First identify which main line it follows, because a sister line beside the life line reads differently from one beside the heart or head line.

If it runs inside the life line near the thumb, many palmists call it an inner life line, support line, guardian angel line or Line of Mars.

Its clarity and the section it covers matter more than the label. A faint short sister line should not be turned into a dramatic promise.