So, how many ratios pertaining to the sides of the triangle are possible? Let's take a look:

What possible ratios
of the sides
exist?

If we flip these three ratios over, we have three more:

The first three ratios established above have specific "names" (sine, cosine and tangent). These are referred to as the basic trigonometric functions.
Sine (sin) 
Cosine (cos) 
Tangent (tan) 



The second three ratios established above also have specific "names" (cosecant, secant, and cotangent). These three ratios are referred to as the reciprocal trigonometric functions.
Cosecant (csc) 
Secant (sec) 
Cotangent (cot) 



Notice that these three new ratios are reciprocals of the ratios of the basic trigonometric functions.
Applying a little algebra shows the connections between these functions.
Applying this connection will create some basically used statements about trigonometric ratios:
Trigonometric functions work ONLY in right triangles! 