For the compound:

A gas is said to be at standard state conditions if the pressure of the gas is 1 atm.

A solute is said to be at standard state conditions if the the concentration of the solute is 1 M.

Pure solids and liquids are in there standard states.

For the elements:

The statndard state of an element is the state in which the element exists at 1 atm of pressure and 25 °C. (By the way, standard state conditions are different than STP.)