in general, tender offer is normally means An offer to purchase some or all of shareholders' shares in a corporation. The price offered is usually at a premium to the market price, and it refer to open, and it an exchange offer,

要约收购 is normally use for Public Company, like if a corporation's stock value is $1/share, an buyer might offer $1.15/share to its shareholders , on the condition that 51% of shareholders agree the offer will be consent and execute.

but 标购 is more about passivity purchase, like if ford will to sell land rover, then other corporation will offer a price, and ford will consider all the tender price from other company.