(1):

(n.) A somewhat similar set of changes taking place in the High German dialects (less fully in modern literary German) from the 6th to the 8th century, known as the second Lautverschiebung, the result of which form the striking differences between High German and The Low German Languages. The statement of these changes is commonly regarded as forming part of Grimm's law, because included in it as originally framed.

(2):

(n.) The regular changes which the primitive Indo-European stops, or mute consonants, underwent in the Teutonic languages, probably as early as the 3d century b. c. , often called the first Lautverschiebung, sound shifting, or consonant shifting.