The reinforcement bars come in certain lengths. This length may not be sufficient.
In tall buildings, there may arise a situation where the length of the rebar in the column may not be sufficient. To meet the need, we will have to overlap the existing rebar with a new one. The length to which they are overlapped is called Lap length. Lap length should be provided in such a way that the load is transferred safely to the new bar. Here transfer is from steel to steel.
The bond between steel and concrete is very crucial for the performance of a structure. The length of a member required to develop the full bond is called the anchorage length. The bond is measured by bond stress. In the above diagram, you can see the difference between a beam with and without development length.