(usually in the plural) A leading or primary principle, rule, law, or article, which serves as the groundwork of a system; an essential part

“one of the fundamentals of linear algebra”

The lowest frequency of a periodic waveform.

The lowest partial of a complex tone.

The fundamental analysis data.

“While this stock has been trading at a low P/E multiple lately, I think its fundamentals are sound, and consider it a good buy for long-term investors.”