Often used in contrast with 短, especially in expressions like 長と短 or 長短. As a standalone everyday word, 長所 is usually more natural.
See also: 短
両案にはそれぞれ長と短がある。
Both proposals have their respective strengths and weaknesses.
noun
superiority; being ahead
Limited use for superiority or advantage, especially in the fixed expression 一日の長がある, meaning to have an edge through greater experience or skill.
経験の差で、彼には一日の長がある。
Because of the difference in experience, he has an edge.
noun
Music term used in contrast with 短 for major versus minor keys. It is normally seen in compounds such as 長調 and ハ長調 rather than as a free standalone noun.
See also: 短
この曲はハ長調で書かれている。
This piece is written in C major.