[AIVC, Air infiltration and ventilation glossary, 1992]:
the leakage of air in or out of a building or space usually driven by artificially induced pressures.(see pressurization test)

[EN 16798-3:2017, 9]:
unintended airflow through leakage paths in the system. (LEA; colour Grey)

[EN 12792:2003, 25]:
unwanted air flow paths in the installation (coded grey)