Space

Perfectly "empty" space will always have VacuumEnergy, the HiggsField, and SpacetimeCurvature. More typical vacuums, such as in outer space, also have gas, dust, wind, light, electric fields, magnetic fields, cosmic rays, neutrinos, dark matter, and dark energy. Despite all these things zipping around in outer space, space does seem empty to earth-bound humans who are used to a dense layer of air to swim around in. These concepts are summarized in the list below.

Matter

Examples: tangible objects, gas, dust, solar wind, cosmic rays, muons
Removability: removable using thick walls and vacuum pumps

Light

Examples: starligt, thermal radiation, cosmic background radiation, radio waves, electromagnetic fields
Removability: mostly removable using thick conducting walls near absolute zero

Neutrinos

Examples: solar neutrinos, neutrinos from radioactive dust
Removability: removable using walls thicker than the earth

Dark Matter

Examples: galactico halos, intergalactic filaments
Removability: unknown, likely not removable

Vacuum Energy

Examples: sea of continual particle pair production
Removability: not removable

Higgs Field

Examples: Higgs coupling, Higgs bosons
Removability: not removable

Spacetime Curvature

Examples: gravity, cosmic structure, dark energy
Removability: not removable

Reference: What keeps space empty?