apparent (quantity)

https://doi.org/10.1351/goldbook.A00418
A term, indicated by a superscript ', which means that a process is not well known or that its value carries uncertainties which are not known, e.g. ΔG is the apparent standard Gibbs energy change. In the context of
partial molar quantities
the word is used in a different sense; as a symbol for 'apparent' in this connection the use of subscript φ, as in Yφ, is recommended. Other notations employed for this property include φX and φX.
Source:
PAC, 1986, 58, 1405. (Recommendations for the presentation of thermodynamic and related data in biology (Recommendations 1985)) on page 1408 [Terms] [Paper]