tan means tangent. In the right-angled trigonometric function, the ratio of the side corresponding to the acute angle to the other right-angled side

cos means cosine, the right-angled side adjacent to the acute angle. The ratio to the hypotenuse

sin means sine, the side corresponding to the acute angle and the side of the hypotenuse

Extended information:

In a right triangle, when The line connecting three points A, B, and C on the plane, AB, AC, and BC, forms a right triangle, in which ∠ACB is a right angle. For ∠BAC, if the opposite side (opposite) a=BC, the hypotenuse (hypotenuse) c=AB, and the adjacent side (adjacent) b=AC, the following relationship exists:

"Sine" in trigonometry The concepts of " and "cosine" were first introduced by Indian mathematicians. They also created a more accurate sine table than Ptolemy.

We already know that the chord table created by Ptolemy and Hipparchus is a full chord table of a circle, which corresponds to the arcs of the arcs and the chords sandwiched by the arcs. Indian mathematicians are different. They correspond the half chord (AC) to half of the arc (AD) of the full chord, that is, AC corresponds to ∠AOC. In this way, what they create is no longer a "full chord table", but a "whole chord table". It's a "sine table".

Indians call the string (AB) connecting the two ends of the arc (AB) "jiba", which means bow string; they call half of AB (AC) "alhajiba". Later, when the word "Jiva" was translated into Arabic, it was misunderstood as "bend" or "recess", and the Arabic word was "dschaib". In the twelfth century, when the Arabic was translated into Latin, the word was translated into "sinus".

Reference material: Trigonometric functions-Baidu Encyclopedia