Fruit tree questions

[Legg Creek Farm]

We recommend that you look at rootstocks and chill hours of the fruit tree varieties that you’re planting. For us here in Texas, chill hours impact what we can grow and where.

 

[Tim Horton]

......Chill Hours..... That is a term I have not heard of before.. I presume that has to do with temps after the tree, bush, plant has produced fruit before it will flower and fruit again.. ?? I can only imagine the growing zone has a lot to do with that cycle ??

Please explain...

Disclaimer.. Remember, I'm the Websters definition of ..black thumb..
Thanks