- 'x' stands for 'position' measured on some line of space, i.e.: position on ONE Dimension or "AXIS" (such as the X-axis) of space.
- 't' stands for 'time'.
- 'v' stands for 'velocity'.
- Any variable name or symbol written with a horizontal bar above it stands for the average value of that variable (over some time interval).
v with a bar above it refers to 'average velocity', etc.
- A symbol written without a bar above it refers to the variable value at one instant in time.
v with nothing above it refers to 'instantaneous velocity'.
- If the subscript zero is seen to the right of a symbol, then the symbol refers to the variable value at t=0.
In other words, it refers to the instantaneous value of that variable at the beginning of whatever period of time we're interested in.
v0 is read 'v-naught' and means the starting or 'initial' value of velocity.
This is a particular example of instantaneous velocity.