Infitah means openness and is opposed to itbaq. It describes the lack of the particular enclosed tongue–palate configuration associated with ص، ض، ط، ظ.
All letters other than those four belong to infitah. Importantly, ق، غ، خ are elevated (istiʿla) while remaining open (infitah). Thus istiʿla and itbaq are not interchangeable terms.
Practice: articulate ق from its correct place with its elevated quality, but do not impose the specific enclosure of ط upon it. Comparing the two shows how several qualities combine to give each consonant a distinct identity.