ulimit -T "threads not supported" with ksh

Issue

• What is "threads" from the output of ulimit -a in below output? Why is it not supported? Also, where do you set this since /etc/security/limits.conf doesn't show that entry.

# ulimit -a
address space limit (kbytes)   (-M)  unlimited
core file size (blocks)        (-c)  0
cpu time (seconds)             (-t)  unlimited
data size (kbytes)             (-d)  unlimited
file size (blocks)             (-f)  unlimited
locks                          (-L)  unlimited
locked address space (kbytes)  (-l)  64
nice                           (-e)  0
nofile                         (-n)  1024
nproc                          (-u)  1024
pipe buffer size (bytes)       (-p)  4096
resident set size (kbytes)     (-m)  unlimited
rtprio                         (-r)  0
socket buffer size (bytes)     (-b)  4096
stack size (kbytes)            (-s)  10240
threads                        (-T)  not supported
process size (kbytes)          (-v)  unlimited