Literally, 'homage (or praise) to'. Also a short Pali expression offered in praise of the Buddha by Buddhists in the Theravada tradition. One of the most common Theravada Buddhist chants or prayers. It traditionally precedes other verses or offerings, and often appears on the title page of books written by Buddhist monks or lay followers. In Romanized Pali, the verse is:
Namo tassa bhagavato arahato samma-sambuddhassa

There are several names for this verse; it is called the Preliminary Formula for Revering the Buddha, the preliminary formula, the verse in praise of the Buddha, etc. But the shortest and most memorable name is simply 'Namo', taken from the first word of the verse. It dates from the scriptures of the Pali Canon, where there are records of students of the Buddha reciting this verse to express their devotion to, or appreciation of, him and his teachings. Like most short Buddhist chants, it is usually repeated three times. It is said that this is because if something is repeated thrice, the odds are that at least one time in three you will actually have your mind on what you are doing! In translation, it reads:

Namo tassa bhagavato
I (we) wish to revere with body, speech and mind that Lord apportioning Dhamma

arahato
that One far from defilements

samma-sambuddhassa
that One Perfectly Enlightened by himself.

It can alternately be translated more simply as:
Homage to the Blessed One, the Worthy One, the Rightly Self-awakened One.
The first translation is seen by some as being more symbolic. The three names given to the Buddha (bhagavato, arahato, and samma-sambuddhassa) represent three characteristics of the Buddha: his compassion in teaching the Dhamma, his purity of thought and deed, and his wisdom.

Bhikkhu Khantipalo's book Lay Buddhist Practice provided the first translation and much of the information here. The second translation is that used by the Dhammayut Order in its English-language chanting guide. Both works are available at Access to Insight.