Reciprocating motion

An inline four cylinder combustion engine 

http://www.engr.utexas.edu

Many descriptions of this type of motion include forward & backwards,  up and down , side to side but in a straight line. It repeats itself  over and over’

In the two examples   the pistons move up and down during operation and their motion is described as a reciprocating motion.

The connecting rod converts this motion into a rotary motion through a crankshaft at the output.

http://aeromuseum.org/HomePage.htm

Oscillating motion

http://robotics.ee.uwa.edu.au

An Oscillating motion is one that moves forwards and backwards in an arc or circle repeatedly. It is different from the reciprocating motion in which motion is forward and backwards but in a straight line repeatedly.

in the example on the left the pendulums swing forward and backwards in an arc as does the rocking chair on the right.

http://www.dollhouseandcraft.com

Motion in a straight line is the most basic motion. It is in a straight line, hence the name linear  motion.

 Each footstep you take is a straight line between your feet, whether you walk around a roundabout or walk all the way to Stongehenge. (unless of course you were there in which case you would be motionally stationary.)

When something rotates along the path of a perfect circle it is said to experience rotary motion. The object can spin either clockwise or anticlockwise.

The abbreviation  RPM is quite common and it means Revolutions per minute, in other words rpm indicates the number (or fractions) of circles a spinning object rotates in a minute.