The <Leader> key is mapped to \ by default. So if you have a map of <Leader>t, you can execute it by default with \+t. For more detail or re-assigning it using the mapleader variable, see
:help leader
To define a mapping which uses the "mapleader" variable, the special string
"<Leader>" can be used. It is replaced with the string value of "mapleader".
If "mapleader" is not set or empty, a backslash is used instead.
Example:
:map <Leader>A oanother line <Esc>
Works like:
:map \A oanother line <Esc>
But after:
:let mapleader = ","
It works like:
:map ,A oanother line <Esc>
Note that the value of "mapleader" is used at the moment the mapping is
defined. Changing "mapleader" after that has no effect for already defined
mappings.