TF cards v MicroSD

Wherever I look on the internet I read that there is no difference between TF cards and MicroSD cards.
But I have never been able to boot any of my various Pi using TF cards.
They just do not boot!
What am I missing?
(Apart from not seeing the letters TF in the adverts)!
--
Nev
It causes me a great deal of regret and remorse
that so many people are unable to understand what I write.