Yes, it is indefinite or imperfective aspect of multidirectional verb. When we speak about an action in the past in a general sense, even if the action finished, but the result is not important for us, we use imperfective aspect. Что ты делал сегодня? Я читал книгу, убирался в комнате, ходил в кино. (Прочитал ли книгу до конца, всё ли комнате убрал (убирать (imperf) / убрать perf.) - это не важно.)

This sentence is definite, because we have people who commit an action. In this occasion it's WE(МЫ). Sentences are indefinite when people, who commit an action, are not called. For example: ЗА СТЕНОЙ ПОЮТ. I do not know if there is a similar grammatical construction in English. But, this can be translated: (THEY) SING BEHIND THE WALL.

John, you see that both "мы пошли" and "мы ходили" imforms the listener of that you went to there. Consider these: "Приходи завтра в гости. Я испеку пирог." - Perfective is used for success, result. "Приходи завтра в гости. Я буду печь пирог." - Imperfective for _process_. Baking a cake is a funny activity. You can join! "Приходи завтра в гости. Я буду печь пирог." - Imperfective for process. I _plan_ doing this. I use imperfective jsut because when I'm speaking I think about the process. "испеку" describes baking as a single action. "буду печь" describes a process, the time WITHIN this action. Both hint on that after this there will be a cake (though the first one is more like a prmice of success:)) and that you can eat it. They are different in how the speaker thinks of that: Does he/she thinks of how he/she will be doing this, enjoying this, occupied with this? Or does he/she 'pack' the action in ( ) - an event in ( )'s such, that there is no cake before, but there is a cake after? How did you spend the day? What were you doing? "Мы вчера ходили в кино." "Я чинил сарай". Did you do/have you done anythign great yesterday? "Я починил сарай". How did you spend the day? "Мы сходили в кино, затем поужинали..." --- we did this, and then we did that. "Мы ходили в кино, затем..." --- the same but the speaker imagines it not as a sequence of "events", but as a sequence of timespans: from 5 till 7 we were doing that, from 7 to 8 were doing this, and then...

What your website most probably means is that the sentence is in the past simple tense, sometimes confusingly called past indefinite tense, or the verb ходили is in the imperfective aspect, sometimes called indefinite aspect.

Nevermind, I got it wrong :)