Legended
Attaches legend or label to any expr
Legended[expr_, lbl_ | legend_]
One can use it to provide legend entries for specific elements
PieChart[{1, Legended[2, "Bob"], 3, Legended[4, "John"]}]
Add a legend to a table of numbers
Legended[ Grid[Partition[ Table[If[PrimeQ[n], Item[n, Background -> LightBlue], n], {n, 100}], 10], Frame -> All], SwatchLegend[{LightBlue}, {"prime numbers"}]]
note
Legended is used implicitly with provided options PlotLegends
Plot[{BesselJ[2, x], BesselJ[3, x]}, {x, 0, 20},
PlotLegends -> Placed["Expressions", {Right, Top}]]
Legend placement
Use Placed to adjust the position of your legend, i.e.
Legended[1/2, Placed[SwatchLegend[{Red}, {"Number"}], Before]]