Hello. I just had what looked like stomach lining or something from my insides in my stool. I'm just wondering what this could mean. Thank you.

Hard to tell. .. I feel we can be pretty sure that what you saw in your stool is not the lining of your stomach. That leaves us with the question of " what was it? " As long as you are not having any other symptoms of any problem, you are most likely fine. I'd recommend seeing your doctor to discuss this. You could describe what you saw and maybe get a better answer. A photo, though "gross", would be helpful.