LTR can mean:

• Looptroop Rockers, a Swedish hip hop group.
• Lost time rate, time lost due to HSE incidents in the workplace
• Load task register, a computing instruction
• Logic Trunked Radio, a computer-controlled radio system
• Long terminal repeat, a DNA sequence found in retroviruses and retrotransposons
• Left to right, a group of writing systems
• "Left to Right", a short story by Isaac Asimov
• Letter (paper size)
• London Turkish Radio
• "Laid to Rest", a song by Lamb of God
• Long-term relationship
• Model 700P Light Tactical Rifle, a rifle manufactured by Remington Arms
• Low temperature radiator, a secondary automotive component usually used to cool secondary engine components, like Charge Air Coolers or EGR Coolers
• Liter or litre, a metric unit of volume

The litre (International spelling) or liter (American spelling) (SI symbols L or l, commonly, but incorrectly, abbreviated as ltr) is an SI accepted metric system unit of volume equal to 1 cubic decimetre (dm³), 1,000 cubic centimetres (cm³) or 1/1,000 cubic metre. A cubic decimetre (or litre) occupies a volume of 10×10×10 centimetres (see figure) and is thus equal to one-thousandth of a cubic metre.