What is Penetration?

Legal Definition
Crimes. The act of inserting the penis into the female organs of generation. 9 Car. & Pa 118; S. C. 38 E. C. L. R. 63. See 8 Car. & Payne, 614; 34 E. C. L. R. 562; 5 C. & P. 321; S. C. 24 E, C. L. R. 339; 9 C. & P. 31 Id. 752; 38 E. C. L. R. 320. But in order to commit the crime of rape, it is requisite that the penetration should be such as to rupture the hymen. 5 C. & P. 321.

2. This has been denied to be sufficient to constitute a rape without emission. (q. v.) Bee, on this subject, 12 Co. 37; Hawk. bk 1, c. 41, s. 3; 1 Hale, P. C. 628; 1 East, P. C. 437, 8; Russ & Ry. C. C. 519; 6 C. & P. 351; 5 C. & P. 297, 321; S. C. 24 E. C. L. R. 339; 1 Chit. Med. Jur. 386 to 395; 1 Virg. Cas. 307; 4 Mood. Cr. Cas. 142, 337; 4 Car. & P. 249; 1 Par. & Fonbl. 433; 2 Mood. & M. C. N. P. 122; 1 Russ. C. & M 560; 1 East, P. C. 437.
-- Bouviers Law Dictionary
Legal Definition
A term used in criminal law, and denoting (in cases of alleged rape) the insertion of the male part into the female parts to however slight an extent; and by which insertion the offence is complete without proof of emission. Brown.
-- Black's Law Dictionary
Legal Definition
The entering to that extent to which the defendant’s person must enter that of his victim in the crime of rape.
-- Ballentine's Law Dictionary