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An iron hydride is a chemical system which contains iron and hydrogen in some associated form.
Because of the common occurrence of those two elements in the universe, possible compounds of hydrogen and iron have attracted attention. A few molecular compounds have been detected in extreme environments or detected in small amounts at very low temperatures. The two elements form a metallic alloy above 35,000 standard atmospheres of pressure, that has been advanced as a possible explanation for the low density of Earth's "iron" core. However those compounds are unstable when brought to ambient conditions, and eventually decompose into the separate elements.
Small amounts of hydrogen are absorbed into iron as it solidifies from molten state. Although the H2 is simply an impurity, its presence can affect the mechanical properties of the material.
Despite the fleeting nature of binary iron hydrides, there are many fairly stable complexes containing iron-hydrogen bonds.