Centre-to-centre distance is a concept for distances, also expressed as hart distance. It is also called pitch.

It is the distance between the centre (the heart) of a column or pillar

Column

A column or pillar in architecture and structural engineering is a vertical structural element that transmits, through compression, the weight of the structure above to other structural elements below. For the purpose of wind or earthquake engineering, columns may be designed to resist lateral forces...

 and the centre (the heart) of another column or pillar

Column

A column or pillar in architecture and structural engineering is a vertical structural element that transmits, through compression, the weight of the structure above to other structural elements below. For the purpose of wind or earthquake engineering, columns may be designed to resist lateral forces...

. By expressing a distance in c.t.c., one can measure distances between pillar

Column

A column or pillar in architecture and structural engineering is a vertical structural element that transmits, through compression, the weight of the structure above to other structural elements below. For the purpose of wind or earthquake engineering, columns may be designed to resist lateral forces...

and columns with different diameters without confusion.