What is the meaning of word 'rate' in physics? Often, I have seen in physics the rate of change of velocity or something like that in kinematics. And in question based on speed, time and distance. I would like to know the meaning of the word rate and also the word rate with respect to velocity or any other term.
 A: In physics, rate means rate of change. Basically, how much a certain quantity changes with respect to another quantity that is also changing. You may also sometimes hear the term gradient which describes the same thing. And mathematically, it is also a ratio, say for example
$$\frac{\Delta F}{\Delta t}$$
where the numerator is one physical quantity and the denominator is another physical quantity.
For the examples you ask for, velocity, we would define this ratio
$$\frac{\Delta x}{\Delta t} = v$$
where the quantities in this rate or ratio are $x$ which represents distance and $t$ is the velocity. You have a change of position divided by a change of time. The symbol $\Delta$ literally means change.
Sometimes we wish to calculate this ratio at an instant in time and to do this we take limits (where the denominator and numerator become vanishingly small - I assume you have some knowledge of calculus) and so the instantaneous velocity at an instant in time is
$$v = \frac{dx}{dt}$$
Other examples include acceleration, which is given by
$$ a = \frac{dv}{dt}$$
Another non-dynamics examples of rate could be something like a temperature gradient which could look something like
$$G = \frac{\Delta T}{\Delta h}$$
which could describe how temperature varies with height in a particular region. Here $T$ is temperature and $h$ is height.
Wikipedia has a nice explanatory article on the term rate here. The first paragraph states
“In mathematics, a rate is the ratio between two related quantities in different units.[1] If the denominator of the ratio is expressed as a single unit of one of these quantities, and if it is assumed that this quantity can be changed systematically (i.e., is an independent variable), then the numerator of the ratio expresses the corresponding rate of change in the other (dependent) variable.”
