一块 is a numeral-classifier phrase (一 + 块) that literally means 'one piece' or 'one chunk' and is used for flat or block-shaped objects (一块蛋糕, 一块钱). In colloquial speech it often means 'one yuan' (the basic unit of Chinese currency). Figuratively, preceded by a specifier like 这 or 那, it can refer to a specific area, aspect, or dimension (这一块). Note that 'together' is 一块儿 (yīkuàir) with a retroflex suffix — this entry covers the non-erhua form.