bootstrap what does col-md-4 mean code example

Example 1: col-md bootstrap 4

<div class="row">
    <div class="col-xs-12 col-md-8">.col-xs-12 col-md-8</div>
    <div class="col-xs-6 col-md-4">.col-xs-6 .col-md-4</div>
</div>
<div class="row">
  <div class="col-xs-6 col-md-4">.col-xs-6 .col-md-4</div>
  <div class="col-xs-6 col-md-4">.col-xs-6 .col-md-4</div>
  <div class="col-xs-6 col-md-4">.col-xs-6 .col-md-4</div>
</div>
<div class="row">
  <div class="col-xs-6">.col-xs-6</div>
  <div class="col-xs-6">.col-xs-6</div>
</div>

Example 2: col-md-6 bootstrap

<div class="col-lg-2 col-md-4 col-sm-3 "> Your Stuffs </div>

/*
col-lg  for large

col-md for med 

col-sm for small 

enjoy :) 
*/