Is it okay to train the abs every day?

Yes, it can be okay to train the abs everyday, provided that the ab exercises you do vary in both intensity and type. For example, on Monday you can do ab exercises that help to improve core strength such as a cable rotations, Tuesday you can perform exercises geared more toward improving core stability such as the prone-iso ab (plank), and Wednesday you can perform exercises that enhance core power such as a medicine ball pullover throw.

While you may be able to get away with training your abs every day of the week, my question is "Why would you want to"? Most novice exercisers share a similar goal: To reduce body fat and/or lose weight. Unless you are an elite athlete or professional gymnast, daily abdominal training can be counterproductive.

There is a popular misconception that abdominal training leads directly to body fat reduction in the midsection. Unfortunately spot reduction is not possible, and no amount of ab exercise can accomplish this feat on its own. To reduce body fat you must burn more calories than you take in, and abdominal exercise does very little to burn calories. Theoretically, you could train your abs 7 days a week and have the world's strongest core, but if you carry excess body fat around your belly, no one would ever know it.

Yes, ab training is important, and you should certainly allow some time for it during your training week, but not everyday. Spend the majority of your workout time on exercises that will burn calories (cardio), and exercises that will speed your metabolism (resistance training), that way you can actually see the results of your hard work.

It should be okay to train Abs daily, but not necessary.  The Abs can be trained more frequently than other muscle groups and can often benefit from frequent training but at the same time, rest and recovery is not a bad idea.  Choose 2-3 exercises doing 2-3 sets each and train 2 days on 1 day off or every other day.

Work your abs two to three non-consecutive days a week, taking care to target all your abdominal muscles. Your best program will include working your abs,obliques and back in multiple positions - standing up, in extension, and in rotation. Always do exercises that work all three parts for the best results.