Beginning of the week / end of the week
周末 zhōu mò : The weekend
周初 zhōu chū : The beginning of a week

Note:

In general, 周末 refers to Saturday and/or Sunday clearly, while 周初 is a little ambiguous. 初 means &quot;the beginning&quot;, and 周初 could refer to Monday or Tuesday or even Wednesday. You could say “星期三左右&quot; to mean &quot;days around Wednesday&quot;. ”左右&quot;(zuǒ  yòu) means &quot;approximate,around, about&quot;.
You could say “月末(=月底),年末(=年底=岁末),周末,期末(qī mò,= the last few days of a semester in school)&quot;,but don't say &quot;期底&quot; or &quot;周底&quot; or&quot;岁底&quot;. That sounds wierd.