Limit -

Infinitesimal - an infinitely small number, often represented by dx and dy. dx/dy is their ratio.

Limits - small numbers represented by epsilon, delta. Describe the value of a function at certain input in terms of its values at a nearby input.

Liebniz
Introduced elongated s symbol, from the word sum, now the integral symbol, realizing that the area under the curve us a summation, whereas the tangent of the curve is a difference.