At its core, the meaning of sp^n is that one s orbital mixes with n number of p orbitals close in energy to form degenerate (same-energy) hybridized atomic orbitals that can allow access to more electrons than available from "pure" (s, p, etc) atomic orbitals for bonding.
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sp^3 bonding involves using four sp^3-hybridized atomic orbitals, so it must have four electron groups. EX: "CH"_4
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sp^2 bonding involves using three sp^2-hybridized atomic orbitals, so it must have three electron groups. EX: "BH"_3, "H"_2"C"="CH"_2
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sp bonding involves using two sp-hybridized atomic orbitals, so it must have two electron groups. EX: "H"-"C"-="C"-"H", :"C"-="O":
I've explained sp^3 and sp^2 hybridization below, and from that, I think you can imply what sp hybridization is.
\mathbf(sp^2)-HYBRIDIZED BONDING
For instance, "H"_2"C"="CH"_2 involves two sigma bonds (one for each single bond), and then one sigma and one pi bond (used in one double bond), so three electron groups are needed, but 4 electrons need to be donated by carbon.
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Since carbon has 4 valence electrons, but its p orbitals (which are highest in energy) only contain 2, it needs to mix two of the three 2p orbitals with the 2s orbital to make use of 2 more valence electrons. This is favorable because it involves the lowering of the energies for two of the 2p orbitals, increasing stability.
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This results in the usage of three sp^2 hybrid orbitals to bond: the ones with one electron for sigma bonding to hydrogen, and the one with two electrons for incorporating one sigma and one pi bond with the other carbon.
1 2s orbital had been incorporated, and 2 2p orbitals had been incorporated, so it is called sp^2, having 33% s character and 66% p character.
\mathbf(sp^3)-HYBRIDIZED BONDING
A similar reasoning follows for sp^3 bonding. Let's take "CH"_4 as an example. It needs four electron groups, and it needs to make four IDENTICAL sigma bonds (one for each single bond).
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4 valence electrons are needed from carbon, but only 1 electron needs to be contributed per sigma bond. So, we need four separate degenerate hybrid orbitals to make each sigma bond. Therefore, all three 2p orbitals must mix with the 2s orbital and stabilize in energy overall to get four degenerate hybrid orbitals.
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This results in the usage of four sp^3 hybrid orbitals to bond: the ones with one electron allow sigma bonding to hydrogen.
1 2s orbital had been incorporated, and 3 2p orbitals had been incorporated, so it is called sp^3, having 25% s character and 75% p character.
I think from here, you can imply what sp hybridization means. (Hint: It can also be called sp^1 hybridization.)
