What is the meaning of Hydrogen?

The lightest chemical element (symbol H), with an atomic number of 1 and atomic weight of 1.00794.

  1. An atom of the element.

An atom of the element.

Molecular hydrogen (H2), a colourless, odourless and flammable gas at room temperature.

  1. A molecule of this molecular species

A molecule of this molecular species

The isotope hydrogen-1 (also symbol H), contrasting with deuterium and tritium

A sample of the element/molecule.

hydrogen

hydrogen (chemical element, symbol H)

hydrogen (chemical element, symbol H)

hydrogen

Source: wiktionary.org