What the entry says.
Discipline. Traveling in pursuit of Truth. To pursue aikido, or any martial art, as a path to self-improvement involves more than training. The word "shugyo" connotes a continual striving for technical and personal excellence. KEIKO, or training, is only one component of such striving. To pursue aikido as a Way, requires a continual reexamination and correction of oneself, one's attitudes, reactions, dispositions to like or dislike, etc.
My take on shugyo was as hard, severe or intense practice. It takes on connotations of traveling due to the origins of the kanji, however, so I suppose it depends on how we choose definitions. Anyway, my inclination is to say that the "primary" definition would be an intense period of practice or training with the intention of self-improvement. Then in a larger sense saying what was quoted up above. I guess I'm saying the given definition is quite, poetic I guess, but I think incomplete as it misses the more direct meaning of the term.
Maybe someone fluent in Japanese and Martial Arts has insight? Cause that ain't me... So huge grains of salt and all that.