What does LD 50 / LC 50 mean?

LD stands for "Lethal Dose". LD 50 is the amount of a substance given at once that causes death in 50% (half) of a group of test animals. The LD 50 is a way of measuring the short-term poisoning potential (acute toxicity) of a material.

Toxicologists can use many types of animals, but most commonly tests are performed with rats and mice. It is usually expressed as the amount of chemical administered (e.g. milligrams) per 100 grams (for smaller animals) or per kilogram (for larger test subjects) of the test animal's body weight. The LD 50 can be found for any route of access or administration, but dermal (applied to the skin) and oral (given by mouth) administration methods are the most common.

LC stands for "Lethal Concentration." LC values ​​usually refer to the concentration of a chemical in air, but in environmental studies it can also mean the concentration of a chemical in water.

According to the (Organisation for Economic Cooperation and Development) (OECD) Guidelines for the Testing of Chemicals, a traditional experiment involves exposing groups of animals to a concentration (or range of concentrations) for a fixed period of time (usually 4 hours). The animals are observed clinically for up to 14 days.

The concentration of the chemical in the air that kills 50% of the test animals during the observation period is the LC 50 value. Depending on certain laws, other exposure times (compared to the conventional 4 hours) may apply.

The equation used to convert mg/l to ppm is:

mg/l = ppm × molecular weight (MW) / 24,450 

What other toxicity dose terms are used?

Those:  https://www.ccohs.ca/oshanswers/chemicals/ld50.html

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