In planetary classification, some barely habitable planets are classified as Class L. (DS9: "The Ascent")
An example of a Class L planet is Indri VIII. (TNG: "The Chase")
The USS Olympia crashed on a L-class planet in the Rutharian sector in 2371. (DS9: "The Sound of Her Voice")
In an alternate timeline, the USS 'Voyager' crashlanded on a Class L planet near the border of the Alpha Quadrant. (VOY: Timeless)
Background
According to the Star Trek Star Charts, Class L planets are 'Marginal' planets. They have an age that ranges from 4-10 billion years and a diameter between 10,000 and 15,000 km. Marginal planets are located within the Ecosphere of a solar system. They are catagorized by a rocky and barren surface with little surface water and an atmosphere of Oxygen/Argon with a high concentration of carbon dioxide. Native lifeforms are limited to plant life, although the majority of Class L planets are suitable for humanoid colonization