This is the 144th most frequent Chinese word.
张
"张" means "to open, spread, or stretch" and is also a measure word for flat objects (e.g., paper, tables).
Here, '张' is used as a measure word for flat objects such as paper, indicating one piece of paper.
我在桌上放了一张纸。
I placed a piece of paper on the table.
In this usage, '张' is part of a proper noun and functions as a surname.
张老师今天给我们上了一堂有趣的课。
Teacher Zhang gave us an interesting class today.
In this sentence, '张' is part of the verb '张开', meaning 'to open', often used for objects like mouths or hands.