My immediate reaction was… but, there is the Catholic catechism. Wait! Does the Eastern Orthodox have a catechism? So I looked it up and at first you might think, yes it does, these websites are claiming there is. But, when you look closer, you realize that what you really have as a result of such a search is a bunch of different websites by different groups explaining what the orthodox believe and they are on some very different topics – nothing like the RC catechism at all.
How about the RC cathechism, does it say what the soul is? Here it is…
363 In Sacred Scripture the term “soul” often refers to human life or the entire human person . But “soul” also refers to the innermost aspect of man, that which is of greatest value in him, that by which he is most especially in God’s image: “soul” signifies the spiritual principle in man.
364 The human body shares in the dignity of “the image of God”: it is a human body precisely because it is animated by a spiritual soul, and it is the whole human person that is intended to become, in the body of Christ, a temple of the Spirit:
Man, though made of body and soul, is a unity. Through his very bodily condition he sums up in himself the elements of the material world. Through him they are thus brought to their highest perfection and can raise their voice in praise freely given to the Creator. For this reason man may not despise his bodily life. Rather he is obliged to regard his body as good and to hold it in honor since God has created it and will raise it up on the last day.
365 The unity of soul and body is so profound that one has to consider the soul to be the “form” of the body: i.e., it is because of its spiritual soul that the body made of matter becomes a living, human body; spirit and matter, in man, are not two natures united, but rather their union forms a single nature.
366 The Church teaches that every spiritual soul is created immediately by God - it is not “produced” by the parents - and also that it is immortal: it does not perish when it separates from the body at death, and it will be reunited with the body at the final Resurrection.
367 Sometimes the soul is distinguished from the spirit: St. Paul for instance prays that God may sanctify his people “wholly”, with “spirit and soul and body” kept sound and blameless at the Lord’s coming. The Church teaches that this distinction does not introduce a duality into the soul. “Spirit” signifies that from creation man is ordered to a supernatural end and that his soul can gratuitously be raised beyond all it deserves to communion with God.
This is an excellent example of what you can expect from the RCC. Compared to other churches it really is an immense giant. Its resources seem nearly endless at times. But that is ok, according to their own rhetoric, they are the church for everyone, so we can use many of those resources too if we like.
I must say… this RC answer is a pretty valiant attempt to get past the difficulties with science, but… Is there ever really something which is not alive and then becomes alive when something is added to it? Nope. The egg is alive, the sperm is alive and the zygote is alive. There is never at any time any point when something becomes alive because of something added to it. In this way the “soul” becomes Carl Sagan’s invisible dragon in the garage, except that while the invisible dragon can still bite you if it chooses, this added “soul” doesn’t do anything at all except serve the rhetoric of those who invented it.