diff --git a/acl/types.proto b/acl/types.proto
index 7e941dc..53f4c5a 100644
--- a/acl/types.proto
+++ b/acl/types.proto
@@ -226,10 +226,10 @@ message BearerToken {
     // Lifetime parameters of the token. Field names taken from
     // [rfc7519](https://tools.ietf.org/html/rfc7519).
     message TokenLifetime {
-      // Expiration Epoch
+      // Expiration epoch, the last epoch when token is valid.
       uint64 exp = 1 [json_name = "exp"];
 
-      // Not valid before Epoch
+      // Not valid before epoch, the first epoch when token is valid.
       uint64 nbf = 2 [json_name = "nbf"];
 
       // Issued at Epoch
diff --git a/object/types.proto b/object/types.proto
index bfb0353..e07a25a 100644
--- a/object/types.proto
+++ b/object/types.proto
@@ -204,7 +204,8 @@ message Header {
   // that affect system behaviour:
   //
   // * __NEOFS__EXPIRATION_EPOCH \
-  //   Tells GC to delete object after that epoch
+  //   Tells GC to delete object after that epoch (but object is available
+  //   throughout the epoch specified in this attribute).
   // * __NEOFS__TICK_EPOCH \
   //   Decimal number that defines what epoch must produce
   //   object notification with UTF-8 object address in a
diff --git a/proto-docs/acl.md b/proto-docs/acl.md
index d434801..d008565 100644
--- a/proto-docs/acl.md
+++ b/proto-docs/acl.md
@@ -72,8 +72,8 @@ Lifetime parameters of the token. Field names taken from
 
 | Field | Type | Label | Description |
 | ----- | ---- | ----- | ----------- |
-| exp | [uint64](#uint64) |  | Expiration Epoch |
-| nbf | [uint64](#uint64) |  | Not valid before Epoch |
+| exp | [uint64](#uint64) |  | Expiration epoch, the last epoch when token is valid. |
+| nbf | [uint64](#uint64) |  | Not valid before epoch, the first epoch when token is valid. |
 | iat | [uint64](#uint64) |  | Issued at Epoch |
 
 
diff --git a/proto-docs/object.md b/proto-docs/object.md
index 2398571..895372b 100644
--- a/proto-docs/object.md
+++ b/proto-docs/object.md
@@ -926,7 +926,8 @@ There are some "well-known" attributes starting with `__NEOFS__` prefix
 that affect system behaviour:
 
 * __NEOFS__EXPIRATION_EPOCH \
-  Tells GC to delete object after that epoch
+  Tells GC to delete object after that epoch (but object is available
+  throughout the epoch specified in this attribute).
 * __NEOFS__TICK_EPOCH \
   Decimal number that defines what epoch must produce
   object notification with UTF-8 object address in a
diff --git a/proto-docs/session.md b/proto-docs/session.md
index 58605b0..cca2d6f 100644
--- a/proto-docs/session.md
+++ b/proto-docs/session.md
@@ -92,7 +92,7 @@ Session creation request body
 | Field | Type | Label | Description |
 | ----- | ---- | ----- | ----------- |
 | owner_id | [neo.fs.v2.refs.OwnerID](#neo.fs.v2.refs.OwnerID) |  | Session initiating user's or node's key derived `OwnerID` |
-| expiration | [uint64](#uint64) |  | Session expiration `Epoch` |
+| expiration | [uint64](#uint64) |  | Session expiration epoch, the last epoch when session is valid. |
 
 
 <a name="neo.fs.v2.session.CreateResponse"></a>
@@ -270,7 +270,7 @@ Lifetime parameters of the token. Field names taken from rfc7519.
 
 | Field | Type | Label | Description |
 | ----- | ---- | ----- | ----------- |
-| exp | [uint64](#uint64) |  | Expiration Epoch |
+| exp | [uint64](#uint64) |  | Expiration epoch, the last epoch when token is valid. |
 | nbf | [uint64](#uint64) |  | Not valid before Epoch |
 | iat | [uint64](#uint64) |  | Issued at Epoch |
 
diff --git a/session/service.proto b/session/service.proto
index 63c238d..e51bd8c 100644
--- a/session/service.proto
+++ b/session/service.proto
@@ -28,7 +28,7 @@ message CreateRequest {
   message Body {
     // Session initiating user's or node's key derived `OwnerID`
     neo.fs.v2.refs.OwnerID owner_id = 1;
-    // Session expiration `Epoch`
+    // Session expiration epoch, the last epoch when session is valid.
     uint64 expiration = 2;
   }
   // Body of a create session token request message.
diff --git a/session/types.proto b/session/types.proto
index eeb869d..4409d15 100644
--- a/session/types.proto
+++ b/session/types.proto
@@ -97,7 +97,7 @@ message SessionToken {
 
     // Lifetime parameters of the token. Field names taken from rfc7519.
     message TokenLifetime {
-      // Expiration Epoch
+      // Expiration epoch, the last epoch when token is valid.
       uint64 exp = 1 [json_name = "exp"];
 
       // Not valid before Epoch