what is a max and min width media query

1/* Max-width */
2@media only screen and (max-width: 600px)  {...}
3
4/* Min-width */
5@media only screen and (min-width: 600px)  {...}
6
7/* Combining media query expressions */
8@media only screen and (max-width: 600px) and (min-width: 400px)  {...}

1@media (max-width: 989px) and (min-width: 768px) {}

1@media (max-width: 991px){
2    .mobile{
3        display: block;
4    }
5}

1/* What this query really means, is If [device width] is less than or equal to 600px, then do */
2@media only screen and (max-width: 600px)  {...}
3
4/* What this query really means, is If [device width] is greater than or equal to 600px, then do */
5@media only screen and (min-width: 600px) {...}