LTR stands for Left to Right and is used as the antonym of RTL, Right to Left, in the context of which direction a script runs on a page or other medium. The majority of modern languages are written LTR. LTR scripts invariably also run top to bottom too, so the text starts and is read from the top left corner, traverses the page to the right margin then returns to the left margin of the line below, as this block of text does.
Tiki assumes all languages are LTR and Themes and Bootstrap format text accordingly. Sripts that run RTL are managed by ... as described in the page How to manage RTL scripts.