What is difference between TS and TR specs in 3GPP?

Hi All,
What is difference between TS and TR specs in 3GPP?
What use for TR?
Like, we have doc for TS in PDF. Do we need to refer TR as well, for day to day work? Is it only for high level?

TR is Technical Requirement.
TS is Technical Specification.

TR comes first.
TS comes on specifications are fixed.
As a protocol tester we refer to TS.

Here you can find a nice conversation with these and other 3GPP terms: 3GPP and ITU Tutorial