We regularly use many references and terms in daily conversation that are abstractions.

For example, we say Today the weather is hot .

"Today" and "weather" are abstractions. Or, to be more precise, they are actually semi-abstractions.

In this case, we are unquestionably relating to physical reality, in the sense that today describes an aspect of the actual physical or dimensional reality that we commonly know and understand as the passage of time.

However, there is no specific material or physical object that we can indentifiably call "today". "Today" is an abstract concept that we easily understand to represent an arbitrarily defined, twenty-four-hour period of time that we are presently in the process of existing in.

The word "today" , therefore, being both an abstract concept, as well as a term describing a physical phenomena, is a semi-abstraction.

As a concept that helps us to temporarily identify a period of passing time, "today" is concrete only as far as the dimension of time is concerned. "Today" does not exist in any other physical or material form.