One of the many ways you can do mass spectrometry.
MALDI stands for Matrix-Assisted Laser Disorption/Ionization. All mass spectrometry methods require a way to take the sample and ionize it. In MALDI mass spectrometry (MALDI MS), the sample is mixed with a carrier or "matrix" and deposited on a target. When the sample is processed, a laser is fired at the sample. The matrix helps the sample boil off the target and get ionized. After that, the electrical field makes the chaged sample ion fly through the machine, and the time-of-flight (TOF) is measured. The TOF gives you a mass/charge ratio, which you then use to get the mass of the sample.
MALDI is pretty quick and easy, but doesn't give you the option of doing tandem mass spectrometry, which is available with other techniques. MALDI is good for quickly getting the mass of your sample.