Metta is different. Metta sounds like meta, which means several things to me: it has its computer meanings (e.g., metadata), its scientific meanings (e.g., metatarsal bones), and other meanings that come from its Greek origins as a prefix meaning after, next to, or regarding the self (e.g., metatarsals are the bones next to or after the tarsals, and meta-emotion is a person's emotion about his/her own emotion).
Metta practice is a meditation on lovingkindness in which one first thinks compassionate thoughts towards oneself (meta-Metta when meta refers to self), then towards someone close (meta-Metta when meta refers to next to), then towards someone who's not as close (meta-Metta when meta refers to after), and then towards everyone (meta-Metta when meta refers to beyond). The bigger picture is that all these various separations—I, you, he, they, others—are artificial. In truth we are not separate from each other, and metta is a way to remember that.
Considering how difficult that concept is, it's easier to start with thinking compassionate thoughts as close as our own hearts, and then letting the compassion spread out in expanding waves just like the ripples of a pebble in a pond. The waves begin at the center place where the stone plops into the water, and then roll out in circles that continue to expand farther and farther way from the center point until they reach to the edges of the pond on all sides. The vibrations never stop until the entire surface of the water has been affected; not only that, they don't even stop at the shore, but bounce back off the edges and ripple back into the middle of the pond again.
