A lower case!

Today in the class of Deal Skills, one classmate raised a question which I totally cannot understand.
After class, I asked him what the question is.
After some more communications, he got to know what I mean and told me that a lower case means the first letter of an English word is not capitalized!
Oh my god, such is the case! I think no single Chinese could understand such an expression of words.
Thanks a lot to the classmate, David.

And one more lessens for me is that today I heard the professor particularly said that trademark refers only to the tangible goods, while service mark refers to intangible things. This made me confused.
After class I went to an American classmate for it. I asked him that in the English world, may "trademark" cover tangible goods and intangible goods? He said he think so but he also showed some hesitation. He said double confirmation would not hurt and let's go to the professor for confirmation. So we went to the professor together. Then the professor told us that trademark covers both tangible goods and intangibles!