Rounding Methods in IEEE
"Floor" and "ceiling" are functions that return the next or previous integral value to a specific float value, where "next" and "previous" are defined with reference to positive infinity. For instance, ⌊2.3⌋ = 2.0, while ⌈2.3⌉ = 3.0. Float values that happen to be an integral value are unaffected.

With that, we can see that "round up" gets the next integral value if the fractional component is 0.5 or greater, otherwise it gets the previous integral value. RU(2.3) = 2.0, while RU(2.7) = 3.0.

The "fix up" is explained in the paragraph after that table, but the definition is a bit erudite. In simple terms, it checks to see that not only if the fractional component is greater than 0.5 (G), but if 1) the integral component is an odd number (L=1) or an even number (L=0), and 2) if the fractional component is exactly equal to 0.5 (S = 0) or if it is greater than 0.5 (s = 1). In effect, RN always rounds to an even number unless it would be specifically closer to an odd number. RN(2.5) = 2.0, RN(2.7) = 3.0, RN(3.5) = 4.0.