a boy, youth, or young man; also a personal attendant or servant, often of junior standing
This word covers two poles of a single social reality: biological youth and dependent service. At one end it names a boy who is still a child, from an infant in a basket to a teenager herding sheep. At the other end it names a personal attendant who belongs to someone's household or service, an armor-bearer, a steward, a traveling companion, a prophet's assistant. Between these poles the senses shade into each other, because in the ancient world a young man of dependent or lowly status and a personal servant occupied the same social ground. The word is often doing both things at once.
The age sense ranges widely: an infant too young to speak (Moses, Ishmael), a boy dedicated to serve at the sanctuary (Samuel), a teenager (Joseph at seventeen), a young man old enough to fight but still contrasted with an experienced warrior. Prophets and kings sometimes use the word to describe themselves as too young for a task. Wisdom literature uses it to address the teachable young man whose character is still being formed.
The service sense also spans a wide range: the unnamed household retainer who carries out an instruction, the dedicated armor-bearer who stays beside his master in battle, the prophet's personal assistant (Gehazi beside Elisha), a steward set over a household or a field. What unites these is dependence and personal attachment to a master. The servant in this sense is not a slave owned as property (that is the word for slave, which occupies a distinct conceptual space) but someone who serves a superior personally and is identified by that relationship.