Question

In Michaelis-Menten Kinetics equation what does "d" stand for? v= d[P]/dt or d[ES]/dt

Answer 1

that d is differential. In calculus it will indicate a infinitesimal change in the value of a function

Answer 2

What does that mean? I never took calculus!

Answer 3

If you understand what is a change in something you may be able to understand the differential.
For example you study from 2pm to 4pm and you solved from the problem 3 to the problem 6 in your chemistry homework. You can said that in that time , 2hs (4pm-2pm = 2hs) you solved 4 problems . That 2 hs time is a time change that you can measure with clock. Then the speed of you solving problems will be equal to
v= 4 problems /2 hours or we can said v=2 problems /1h.
Now if in place to measure big times as 1 or 2 hs we want to express your speed in solve problems at a "instant" time so short that almost cant be measured we use the differential expression that represent the speed in an time very very small that you will be able so solve a very very small part of your 4 problems.
In the case of Michaelis Menten, the differential means the tiny tiny change in the concentration of the product "d[P]" or the complex enzyme substrate "d[ES] in a tiny tiny time "dt". Is like express the change of these concentrations in a instantaneous time.
For your undestanding you can use in place of differential, deltas that is the difference between the final minus the initial value. For example when we calculate the time that you were doing the homework from 2pm to 4pm and we did the difference between them to calculate the time that you spent in the problem solving that is a delta time, in our case 2 h.

Answer 4

http://en.wikipedia.org/wiki/Differential_(infinitesimal)