The zero-width joiner (ZWJ) is a non-printing character used in the computerized typesetting of some complex scripts, such as the Arabic script or any of the Indic scripts. When placed between two characters that would otherwise not be connected, a ZWJ causes them to be printed in their connected forms. In some cases, see the second Devanagari example below, the ZWJ follows the second character being joined rather than coming in between the two characters. The ZWJ's Unicode number is U+200D zero width joiner (HTML: ‍ ‍). In the InScript keyboard layout for Indian languages it is typed by the key combination Ctrl+Shift+1. However many layouts use ']' key for this character.
Read more about Zero-width Joiner: Example