{{ sp | your text goes here }} is a shorthand for {{letter-spacing| your text goes here |0.3em}}, and produces:
साँचा:Sp

Also you can use specified (non-default) value of the gap between letters:
{{ sp | your text goes here | 1em }} is a shorthand for {{letter-spacing| your text goes here |1em}}, and produces:
साँचा:Sp

This shorthand is useful when reproducing old source texts that use spaced-out letters to indicate emphasis. The name is chosen to be similar to {{sc}}.