Maitri (मैत्री, Pali: metta) is the Sanskrit word for "loving-kindness" — the first of the four Brahmavihārās of Buddhism. The benevolent wish that all beings be happy.
The Buddha Maitreya (the future Buddha) is named for her.
Maitri does not currently appear in the US Social Security Administration's top 1,000 girls' names, so we don't publish a US rank or birth count for it. That says nothing about the name's standing elsewhere in the world — only that it sits outside the ranked US data we rely on.
In Pythagorean numerology the letters of Maitri reduce to 7, The Seeker. This is a traditional interpretive system, not a factual claim about the name.