What is the meaning of 'T' in the execution permissions of a directory?

Solution 1:

t takes place of x so you need to be able to distinguish whether the x was supposed to be there and was overwritten by t

• t == sticky + x
• T == only sticky

Solution 2:

Look for sticky bit in here.
Regarding your second question, look at this wikipedia entry on how to set it.

The difference between the two is that 'T' is present

on a file or directory without the execution bit set for the others category

Solution 3:

t will be in place of others permission and in place of execute permission. So it means that t is for execute + sticky bit. T means only sticky bit without execute permission.

Example:

dr-xr-xr-t  2 scm scm 4096 Feb 15 17:48 log
drwxr-xr-T  2 scm scm 4096 Feb 15 18:04 rpm

Here, log has execute + sticky bit (others). rpm has only sticky bit.