[Interest] What does LTS mean?

[Jason H]

I've been encountering an increasing number of issue that are crashes, that become fixed, but not back-ported to 5.12. 

I was under the impression that LTS would include this type of issue. Apparently, I am misinformed. I have reviewed the blog posts:
https://www.qt.io/blog/2015/12/18/introducing-long-term-support (5.6)
https://www.qt.io/blog/2017/05/11/introducing-long-term-support-qt-5-9 (5.9)
https://www.qt.io/blog/2018/12/06/qt-5-12-lts-released (5.12)

In the above I cannot find an itemized description of what LTS constsists of, but I did find in the 5.9 announcement:
Qt 5.6 LTS is in the 'strict' phase where it only receives selected critical fixes and next it is moving into the ‘very strict’ phase. During this final phase, Qt 5.6 LTS will receive important security fixes only.

With Qt 5.12 not being in strict phase (there is no 5.15 LTS yet, and I cannot find an announcement) or even very strict phase, I assume 5.12 is standard LTS phase. I believe fixes for crashes are something that should be in LTSs. Change my mind?

Even if you can change my mind, I am not sure why we even have LTSs in the first place? Can we get a more formal definition of what a LTS is other than "support".