Assalaam alaikum What does The word Alaqa means, some people translate it as leech like substance, and in translations we see it as a "blood clot", The people say, blood clot is not scientific. As there is no blood clot in the formation of embryo... please explain...

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.

Both meanings of ‘Alaqah (clot) are correct. According to Al-Mu'jam Al-Waseet:

Al-‘Alaq (clots): black worms that absorb blood in stagnant water; if an animal drinks them, they stick inside its mouth. The singular form ‘Alaqah (clot)... and (another meaning is) the thick or coagulated blood. Allaah says (what means): {He Created man from a clinging substance [a clot –a piece of thick coagulated blood]} [Quran 96:3]

The ‘Alaqah is a stage of the development of the embryo, and it is the piece of blood from which it is created. Allaah says (what means): {It is He Who created you from dust, then from a sperm-drop, then from a clinging clot.} [Quran 40:67]

The researcher Ashraf ‘Amaashah in his Masters theses entitled “The universe and the scientific vision in the Quran and other divine religions” tackled the subject of the stages of the development of the human creation as it was mentioned in the Quranic verse in which Allaah says (what means): {And certainly did We create man from an extract of clay. Then We placed him as a sperm drop in a firm lodging [i.e. the womb]. Then We made the sperm-drop into a clinging clot, and We made the clot into a lump [of flesh], and We made, [from] the lump, bones, and We covered the bones with flesh; then We developed him into another creation. So blessed is Allaah, the best of creators.} [Quran 23:12-14] He said about the third stage, which is the saying of Allaah {Then We made the sperm-drop into a clinging clot}: "This means that the sperm-drop transforms from its characteristics into the characteristics of a clinging clot, which is the coagulated blood."

In the First World Conference on Scientific Miracles in the Quran and Sunnah, in a Research entitled “Embryology in the Light of the Quran and Sunnah”, the following was mentioned: "The word ‘Alaqah (clot) is derived from the verb (‘Alaqa) which means sticking and clinging to something. The ‘Alaqah is a worm in water; it sucks blood and lives in ponds; it feeds on the blood of animals that it clings to; the plural is ‘Alaq..... The Alaq (clot) is blood in general which is very red, or thick or coagulated. Most interpreters of the Quran referred to this. In addition, the clot refers to moist blood, and this process takes more than a week until the primitive sperm sticks to the placenta by a conductive stem  which subsequently becomes the umbilical cord. During the process of fertilization, the sperm loses its shape to prepare itself to take a new form which is the ‘Alaqah (clot), which begins by the fetus clinging to the placenta. The Quran described this clinging with the word ‘Alaqah. This is consistent with the meaning (clinging to something) which is one of the meanings of the word “clot”.

On the other hand, if we take the literal meaning of ‘Alaqah (clinging worm), we find that the fetus loses its round shape and elongates until it takes the form of the worm, then it starts feeding on the blood of the mother, in the same way that the clinging worm (leech) does, as it feeds on the blood of other organisms. The fetus is totally surrounded by a mucus fluid, just as the leech is surrounded by water. The Quranic word ‘Alaqah shows this meaning clearly according to the appearance and features of the embryo at this stage. According to the meaning "coagulated or thick blood" for the word ‘Alaqah, we find that the external appearance of the fetus and its membranes resemble thick coagulated blood because the initial heart, placenta bag and the cardiovascular veins appear at this stage. The blood is trapped in the blood vessels even if the blood is liquid [not coagulated]; the blood does not begin its circulation until the end of the third week. In this way, the fetus takes the appearance of thick or coagulated blood while it is not coagulated blood, and the aforementioned features fall under the two mentioned meanings of ‘Alaqah: “coagulated blood” or “non-coagulated blood”." [End quote]

Allaah Knows best.