The document discusses the use of "acabar de + infinitive" to express that an action was recently completed in Spanish. It explains that this construction combines the present or imperfect form of "acabar" meaning "to complete" with "de" and the infinitive verb to describe something that just happened. Examples are provided such as "Acabo de terminar mi tarea" meaning "I have just finished my homework" and "Acababa de comer cuando llamó" meaning "I had just eaten when he called."