indentation indentation /ˌɪnˌdɛnˈteɪʃən/

noun

1. () A concave cut into a surface or edge (as in a coastline)  ( indenture , indentation )
   a concave cut into a surface or edge (as in a coastline)
     The typist pressed the keys on the keyboard, leaving an indentation on the paper.
   The typist pressed the keys on the keyboard, leaving an indentation on the paper.
   
2. The act of cutting into an edge with toothlike notches or angular incisions  ( indentation )
   the act of cutting into an edge with toothlike notches or angular incisions
   
3. The space left between the margin and the start of an indented line  ( indent , indentation , indention , indenture )
   the space left between the margin and the start of an indented line
   
4. The formation of small pits in a surface as a consequence of corrosion  ( indentation , pitting , roughness )
   the formation of small pits in a surface as a consequence of corrosion