The movement was obliged to be in triple time; the rest was ad libitum.
机芯必须三倍时间； 其余的是随意的。
中文百科
Ad libitum
Ad libitum是一个拉丁文短语，表示“随意”。Ad libitum常简写为'Ad lib'（作为形容词或动词）或'ad-lib'（作为动词或名词）。这还有个很少使用的同义词a bene placito。
英语百科
Ad libitum
Ad libitum (/ædˈlɪbᵻtəm/) is Latin for "at one's pleasure"; it is often shortened to "ad lib" (as an adjective or adverb) or "ad-lib" (as a verb or noun). The roughly synonymous phrase a bene placito ("in accordance with [one's] good pleasure") is less common but, in its Italian form a piacere, entered the musical lingua franca (see below).