Social mobility simply means the stratification system, particularly as a result of changes in occupation, wealth or income. It is the movement of an individual from one social stratum to another within the occupation, class structure or society.
Kelley (1967) sees social stratification as “the relative location, horizontal and vertical of persons towards each other in terms of the relative ranking of power, wealth and honourwithin the social structure known as the society”.
1.  Vertical Mobility:-
This means the movement of individuals from one social stratum to another social stratum. This type of mobility includes both upward mobility and downward mobility. Upward mobility is an increase in occupational status, moving to higher and more prestigious positions. While the downward mobility is a decrease in occupational status, from someone who is working to an unemployed person.
2.  Horizontal Mobility:-
This simply refers to the movement of individuals within a social stratum. In other words, it is a change in occupation that involves no change in status, example autoworker to steelworker. Horizontal mobility is also known as lateral mobility.