The phrase "meter altitude" refers to the height of something above sea level, measured in meters. It tells you how high an object or location is compared to the average level of the ocean. Full definition
In observations with ALMA (Atacama Large Millimeter / submillimeter Array), a gigantic radio telescope which will be constructed at 5000 - meter altitude in Chile, this generation technique of millimeter / submillimeter wavelengths using the photonic technology will play an important role in detecting faint radio signals from the universe. (alma-telescope.jp)
The subjects reached the outpost at 2650 meters altitude almost effortlessly, by cog railway and cable car, and once there could only take the same number of steps each day that they were accustomed to taking at home, as monitored with a pedometer. (sciencemag.org)
ALMA will be built on the Andean plateau at 5,000 meters altitude near the Atacama Desert of northern Chile. (alma-telescope.jp)