PLA (polylactic acid) is made from biological materials which can be corn starch or sugar cane, which makes it biodegradable. Like other corn or sugar-based materials, it is slowly broken down by many common bacteria. However, it will last a long time under normal conditions, so you have to e.g. do not throw it in the compost pile.
It melts at 180-220 ° C, depending on what other materials are added. PLA begins to deform at temperatures above 60 ° C, it is not water or chemical resistant. PLA has a strong layer bonding, but the material itself is brittle and less elastic.
There is a wide range of PLA mixtures, containing wood, (plastic added to fibers), metal, luminescent (plastic added to phosphorescent pigment). There are variants of PLA that make it both less crispy and more heat tolerant. Some varieties require that you harden them in an oven, to achieve the desired strength. However, this allows the workpiece to shrink slightly, which can be important to take into account if it is a functional part where tolerances are important.
When printed with PLA, it emits a sweet scent. Unlike ABS, it does not emit toxic fumes, so a cabinet is not necessary. In general, PLA is less temperamental and requires a lower temperature to print with than e.g. ABS and does not need a heated print bed.
PLA is generally easier to print with than e.g. ABS or PETG, but finishing is more cumbersome.