This is the 462nd most frequent Chinese word.
這個
"這個" means "this" in English.
In this sentence, '這個' is used as a demonstrative pronoun to specify a particular noun, '蘋果' (apple), indicating one specific apple.
這個蘋果看起來很新鮮。
This apple looks very fresh.
Here, '這個' is combined with '星期' (week) to point out the specific week being referred to, often meaning 'this week'.
這個星期我的行程非常滿。
This week my schedule is extremely full.
In this context, '這個' is employed to identify the specific subject, '問題' (issue), that the speaker is discussing, signifying 'this issue'.