Creating managed metadata Terms using Powershell
#Connect to MMS Site
$taxonomySite = get-SPSite "siteURL"
#Connect to Term Store in the Managed Metadata Service Application
$taxonomySession = Get-SPTaxonomySession -site $taxonomySite
$termStore = $taxonomySession.TermStores["Managed Metadata Service"]
#Connect to the Group and Term Set
$termStoreGroup = $termStore.CreateGroup("Group Name")
$termStoreGroup.Description = "Group description"
$termStoreGroup.AddGroupManager("Domain/User")
$termStoreGroup.AddContributor("Domain/User")
$termSet = $termStoreGroup.CreateTermSet("TestTermset",1033)
#Create term, term description, and a synonym
$term = $termSet.CreateTerm("TestTerm", 1033)
$term.SetDescription("This is a test", 1033)
$term.CreateLabel("This is a test synonym", 1033, $false) | Out-Null
$termStore.CommitAll()