What mean index seek noncluster where select based on mslid?

CREATE TABLE [Parts].[ManufacturingData](
     [LeadFinishId] [int] IDENTITY(1,1) NOT FOR REPLICATION NOT NULL,
     [PartID] [int] NOT NULL,
     [LeadFinishMaterial] [varchar](50) NULL,
     [CreatedDate] [datetime] NULL,
     [CreatedBy] [int] NULL,
     [ModifiedDate] [datetime] NULL,
     [Modifiedby] [int] NULL,
     [DeletedDate] [datetime] NULL,
     [DeletedBy] [int] NULL,
     [Revision_Id] [int] NULL,
     [BaseMaterialID] [int] NULL,
     [MSLID] [int] NULL,
     [MSLSource_Revision_id] [int] NULL,
     [MaximumReflowTemperatureID] [int] NULL,
     [ReflowTemperatureSource_Revision_Id] [int] NULL,
     [MaximumWaveTemperatureID] [int] NULL,
     [WaveTemperatureSource_Revision_ID] [int] NULL,
     [ReflowSolderTimeID] [int] NULL,
     [WaveSolderTimeID] [int] NULL,
     [NumberOfReflowCycleID] [int] NULL,
     [LeadFinishPlatingID] [int] NULL,
     [Comment] [varchar](100) NULL,
     [LeadfinishSourceTypeID] [int] NULL,
     [MSlSourceTypeID] [int] NULL,
     [ReflowTemperatureSourceTypeID] [int] NULL,
     [BasedOnID] [int] NULL,
     [LeadFreeProcessCapabilityID] [int] NULL,
     [BaseMaterialRevisionID] [int] NULL,
     [BaseMaterialSourceTypeID] [int] NULL,
     [UnderplatingRevisionID] [int] NULL,
     [UnderplatingSourceTypeID] [int] NULL,
     [ShelfLifeCondition] [int] NULL,
  CONSTRAINT [PK_PartID] PRIMARY KEY CLUSTERED 
 (
     [PartID] ASC
 )WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [Customer]
 ) ON [Customer]
    
 GO
    
 SET ANSI_PADDING ON
 GO

index seek used as below

 CREATE NONCLUSTERED INDEX [IDX_MSLID] ON [Parts].[ManufacturingData]
 (
     [MSLID] ASC
 )WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, SORT_IN_TEMPDB = OFF, DROP_EXISTING = OFF, ONLINE = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [Customer]
 GO

USE [Z2DataCore]
GO


 ALTER TABLE [Parts].[ManufacturingData] ADD  CONSTRAINT [PK_PartID] PRIMARY KEY CLUSTERED 
 (
     [PartID] ASC
 )WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, SORT_IN_TEMPDB = OFF, IGNORE_DUP_KEY = OFF, ONLINE = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [Customer]
 GO