Mucocele https://en.wikipedia.org/wiki/Oral_mucocele
Mucocele est conditio per extravasationem muci, phaenomenon vel retentio mucosae. Mucoceles caerulei habent colorem translucidum et plerumque inveniuntur in pueris et iuvenibus.

Locus frequentissimus mucocele invenire est superficies interior labii inferioris. Quaedam mucoceles sua sponte post breve tempus resolvunt; alii sunt chronici et remotionem chirurgicam requirunt.

Informationes plurimae ― Latine
References Overview of common oral lesions 36606178 
NIH
The pathologies covered include recurrent aphthous stomatitis, herpes simplex virus, oral squamous cell carcinoma, geographic tongue, oral candidosis, oral lichen planus, pre-malignant disorders, pyogenic granuloma, mucocele and squamous cell papilloma, oral melanoma, hairy tongue and amalgam tattoo.
 Oral Mucosal Lesions in Childhood 36354659 
NIH
Mucoceles Forma cum minor glandulae salivaris laeditur, causando salivam in meatibus obstructis aedificandi. Hae incrementa plerumque sine dolore, levia sunt, et caerulea vel pellucida apparent, 1 cm magnitudine plerumque non excedente. Curatio chirurgicam remotionem involvit, chirurgi quoque interdum glandulas proximas removent ne recursus.
Mucocele develops as a consequence of mechanical trauma to a minor salivary gland, which is followed by saliva retention and accumulation inside the blocked and dilated excretory ducts of the gland. Lesions are usually painless, with smooth surfaces, bluish or transparent. Most are not larger than 1 cm in diameter. They are treated by surgical removal; at that time, the surgeon often decides to perform the ablation of the neighboring minor salivary glands in order to prevent relapses.