The term <em>slang</em> refers to <u>informal language</u> and it is usually considered to carry negative connotation, because it stands out from the standard, formal language.
So the answer here is that the connotation of <em>slang</em> in the second sentence is that:
The word <u>legitimate</u> helps us understand this, that even though slang was considered a bad thing, through time those words gained full meaning and are now commonly used.
The main purpose of the transition word in the sentence: "Meanwhile, Jacey waited for the fitting room to become available." is that it connects a series of similar events. Explanation: Meanwhile can be defined as the time before something happens or before something ends, it is another way to say "during this time".
