I wear golf shoes made by FootJoy — and I like them. They are firm; they shed water well (for early morning golf); they have lasted. The psalmist has another kind of foot joy: “Your statutes (adot) are my heritage forever.” And now this:
“They are the joy of my heart” (119:111).
The light of his feet, the word that guides his path in the darkness and which gets him into all kind of oppressive situations, are his heart’s joy. He’s got the joy of lighted feet; he’s got foot joy. (My new shoes bring me “foot joy.”)

What brings our “moral feet” joy? For the psalmist, it is what he hears from God through Torah as he walks the path of life. He’s resolved; he’s committed forever; he knows the lights that guide his feet are his inheritance and what he will pass on to others — this all brings his feet great joy as he seeks to walk.
The “joy” here is exultation. With joy you will draw water from the wells of salvation (Is 12:3); those who return to Zion will enter with singing and everlasting joy will crown their heads (35:10); “joy and gladness will be found in her, thanksgiving and the sound of singing” (51:3); he also speaks of the “oil of joy” (61:3).
This kind of joy is the eschatological hope of an oppressed people. I suspect it is a special word that an oppressed psalmist was attracted to.