Yesterday is a term that comes from Latin ad heri. It is a concept that can be used as adverb or as noun, always linked to a Preterite time.
The most common use of yesterday refers to day immediately preceding today's day. By example: if today is Friday, yesterday was Thursday. As can be seen, yesterday is the day before the current one.
The preceding day
It can be said that yesterday refers to a very close past. That is why the notion is used frequently in everyday life, since its effects usually continue in force: "Yesterday I hit my leg and it still hurts", "Today I am not going to cook because there was food left over from yesterday", "In my house we have no Internet connection since yesterday".
If we position ourselves in the Present (the today) of a timeline, the day before is the Yesterday, while the one before yesterday is the the day before yesterday. Looking to the future, the day that follows today is the morning and then comes the day after tomorrow.
The temporal order, therefore, is as follows: the day before yesterday - yesterday - today (the current day) - tomorrow - the day after tomorrow.
Yesterday as past in general
The idea yesterday can also be used to refer to a more distant or undefined past. In fact, talking about yesterday makes it possible to mention the weather preterite in its broadest sense.
"The customs of yesterday tend to be strange to us today", "My psychologist told me that I should not live in yesterday since I have to deal with the present" and "His eyes, bright yesterday, have lost their light since the tragedy happened" are expressions who use the term in this way.
The importance of moving forward
From the philosophy, psychology, sociology and other sciences have studied how yesterday affects people and communities. It is usually understood that the present is, to a greater or lesser extent, a consequence of yesterday.
This means that, at a general level, conduct and the feelings of an individual are tied to experiences of his past. Yet yesterday must be "indicted" (understood, accepted) to have a full or peaceful present.
Suppose a man he suffered abuse in his childhood by his parents. That yesterday surely conditioned his development and shaped his personality, but it is not a determining factor so that he is not happy in adulthood or that he cannot build a healthy bond with his own children.
In a society, yesterday is analyzed by historians. Although what happened years, decades and centuries ago is key to understanding the circumstances of the present of a people, it should not be an anchor that prevents moving forward or projecting the future.
"Yesterday" in music
It is interesting to note that many songs they are titled "Yesterday", reflecting the importance of this word. On 1993, two great artists included songs titled this way in their albums: Luis Miguel (On the disk "Aries") and Gloria Estefan (on "My land").
Closer in time Enrique Iglesias recorded "Yesterday" for his record work "Euphoria", which came out to the sale on 2010.
Finally, one cannot fail to mention "Yesterday" ("Yesterday", in our idiom), the classic composed of Paul MCCARTNEY which is part of the album "Help!" from the Beatles.